Software licensing is a contentious subject, and has been debated endlessly for decades. There are hundreds of licenses documented by the SPDX (Software Package Data Exchange), and surely more in existence created ad-hoc for individual projects. Not all of these licenses are free software licenses: some, such as the Business Source License, were written specifically to restrict freedom 0, the freedom to use the software for any purpose, in response to the growth of service providers such as AWS (Amazon Web Services). This post will restrict itself to considering only free software licenses.
I should also preface this discussion by making it clear that I am not a lawyer, and due to the complex nature of copyright law (especially when international laws are taken into consideration), it is quite possible that I will miss some details. Please do not hesitate to contact me (see the footer of this site) if you'd like to make a suggestion or correction.
Traditional software licenses
There are two broad camps within the free software community. In one camp are the "copyleft" licenses, such as the GNU GPL (General Public License). The defining characteristic of copyleft licenses is their requirement that changes made to the software and distributed to users must be made available to those users under the same or similar terms. The scope of these conditions varies between licenses: some, such as the MPL (Mozilla Public License), only requires developers to pass along their freedoms for changes made to the original project, while other components linked to it may remain non-free, while others, such as the AGPL (Affero General Public License), require these freedoms to be passed along for all components of the software even for users only interacting with it over a network (not distributed in the traditional sense). The core argument made by proponents of these licenses is that free software should stay free: using a copyleft license prevents others from taking the hard work of free software developers and turning it into something that no longer respects the fundamental user freedoms offered by the original software.
In the other camp are the "permissive" licenses, such as the MIT License. These licenses do not require developers to pass along their original freedoms in derived projects: usually, the primary requirement of a permissive license is merely to maintain the original license text in copies of the software or derived works. There are several reasons why a developer might choose a permissive license, but usually it boils down to a desire to allow the software to be adopted as widely as possible: even developers of non-free software can incorporate components placed under permissive licenses without needing to distribute some or all of their resulting software under the same license. Permissive licenses are increasingly popular: even back in 2015, usage data reported by GitHub showed a considerable majority of licensed projects using permissive licenses (with the MIT license being the most popular at the time).
Both types of licenses (copyleft and permissive) have unique advantages and disadvantages. A talk by Rob Landley, creator of the "Zero-Clause BSD" License, presents a good overview of some of the disadvantages.
On one hand, copyleft licenses have become increasingly fragmented with the split between versions 2 and 3 of the GPL, which are not compatible unless the author of the software has included the "or any later version" clause in their license notice. Several prominent projects, including Linux, are licensed under GPL v2 only, which makes them incompatible with projects using GPL v3 or later. Code cannot be shared between projects under these licenses, even though both licenses share similar goals and philosophies.
On the other hand, the license preservation condition of most permissive
licenses leads to some rather absurd consequences of its own: a glance at the
"licenses" screen of most commercial products (such as phones, in-car
entertainment systems, etc.) will reveal dozens of almost identical license
texts placed side by side, often differing only in the copyright year and
author. For example, in Arch Linux, each MIT-licensed project must be
distributed with a separate license
file, installed under
/usr/share/licenses, to comply with the letter of the requirement that the
license notice must be preserved.
In reaction to these issues, and driven by a sense of frustration with software licensing as a whole, some users have turned to the public domain for a solution. Works in the public domain are free of any restriction whatsoever: there is not even a requirement to provide attribution to the original author when distributing or modifying the work. Many people are familiar with the public domain through works whose copyright has expired, such as old books, musical compositions, and works of art, and there are "licenses" such as the Unlicense and CC0, which attempt to dedicate works whose copyright would otherwise not have expired into the public domain.
These "licenses" are often fraught with various issues, particularly since not every country has the same concept of "public domain" or whether it is possible for the author of a work to explicitly relinquish the work into the public domain. The Unlicense is known to have several issues, and CC0 has been rejected by some projects, such as Fedora, due to concerns about patent wording in the "fallback" license. Google, for example, has restricted usage of such public domain dedicated software within the company. (The reference to Google's policies here is not meant as an endorsement of all their thoughts on licensing, but if the goal of permissive licenses is to allow wide reuse of software, many other companies and individuals are sure to run into similar concerns, hindering adoption.)
So is there any way to achieve the same freedom of completely unrestricted reuse offered by the public domain in a context where the public domain cannot be used reliably? Rob Landley (cited in the previous section) created the Zero-Clause BSD license (or 0BSD for short), which strips down a traditional permissive license down to its core essential, the grant of the fundamental freedoms of free software:
Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted.
This single sentence, along with the obnoxious but unfortunately necessary ALL CAPS disclaimer of warranty and liability, is the entire license. No requirement to copy around the license text, no requirement to include attribution to the author, only an unrestricted and irrevocable grant of freedom. And, unlike a public domain dedication, this is technically a license: the author is not actually waiving any copyright over the work, just opting out of all the protections that copyright would normally offer. For this reason, it is considered less legally problematic than a public domain dedication: Google, for example, uses the 0BSD-licensed Toybox tool collection in Android.
Opting out of the licensing game
This is why I've chosen the title of this post. When I write software, I want others to be maximally empowered to use, inspect, modify, and distribute my work. I don't want anyone to waste precious hours of their life debating whether or how they need to include a blob of license text in their project just because they copied my code. In this way, my philosophy is reflected perhaps most clearly in the WTFPL, but I also recognize that the copyright system still exists, and I need to operate within its constraints if I want others to be comfortable reusing my work.
I have used several licenses for my projects through my years as a developer, and this is the perspective I have come to over that time as I have struggled with many of the same issues described above (e.g. how to deal with license notices when reusing parts of a project). For me, this is the purest form of free software: software free for all users and all purposes, free from restrictions of any kind, dedicated not to my own self promotion or profit but for the joy of programming and the benefit of the community. As such, I intend to gradually relicense all my own work to the 0BSD license, and my written (non-software) content to CC0 (which is still considered fine for non-software works) for similar reasons. I want to work towards a world where software and creative works as a whole can be maximally free for everyone.