From a user perspective, the license needs no justification, because there is zero restriction on the use of GPL software. From a developer perspective, I respect the choice of the copyright holder. Personally, I have released my own software, but it wasn't under the GPL.
But now it appears Stallman is going to taint other open source products
Here's the magical part of the GPL, and of the like clauses in other OSS licenses. What would be cool is Stallman's ideological followers putting in thousands of man-hours improving their fork, only to have Mozilla re-incorporate those improvements into the main Mozilla-branded version under the GPL-like give-back clause of the MPL. Stallman might as well have handed the Mozilla foundation a bunch of cash.
Mozilla wouldn't have that ability under the BSD license. Stallman's own GPL,in that it inspired those terms of the MPL, is what is keeping him from "stealing" Firefox.
If Iceweasel steals Firefox's marketshare it obviously won't be a benefit to them whether Firefox can use that code or not. You seem to base one's succes on whether you can use the product that replaced them for free or not, in other words according to you SCO should be thrilled that they can use Linux even though it has completely destroyed their Unix business. Yep you probably do think that, business profits mean nothing, free software is all that mattersm just like Stallman believes..