It is sometimes asked, 'why choose AGPL?', or conversely 'why not a weaker copyleft license such as MIT, BSD, LGPL, DWTFYWPL, etc.? While some of the weaker copyleft licenses are apropriate for general utility software, stronger copyright can be an asset in some cases.
There are several benefits people gain through the protections offered by strong copyleft.
Free and Open Source Software can be considered as commonwealth resources. Like any tangible commonwealth resource, such as parks or lakes, software resources can be protected by social norms and regulations. Strong copyleft is essentially a social regulation tool for our knowledge commons.
In order to preserve full access to the commonwealth, explicit requirements are set to ensure the sourcecode will be available to all people. The sourcecode should be accessible through whichever paths people arrive at the software. This means that at any point of contact with the software, people can easily access and view the sourcecode, without having to search elsewhere.
We all enjoy accessing commonwealth resources, and should be permitted to do so. Personal liberties fall within the bounds of the commonwealth protection. This means commonwealth protection takes a higher priority than personal liberty, so that the liberties are guaranteed for all.
Like many physical resources, software needs to be maintained - often by many people. We want to explicitly encourage the maintenance and contribution towards the commonwealth. This is done through the social norm sometimes called 'Share Alike.'
As a project matures, it may come to serve a specific, or niche, purpose. This may be known even in the planning phase. At a certain threshold, strong license protections become increasingly important, just as a large body of water or natural reserve deserves strong regulatory protection.