The AI Lab hackers had free will and were not forced to go anywhere. Saying that these companies "raided" the AI Lab is, quite frankly, insulting. And Symbolics's practice of hiring the hackers full time was actually done entirely for ethical reasons. Other spinoff AI Lab companies were taking advantage of AI Lab resources, and Symbolics wanted to be sure that they didn't do that.
The MIT Lisp Machine code was owned and copyrighted by MIT. When MIT licensed the code to LMI and Symbolics, they wanted to be sure that the code would not be given away for free to other companies, including companies that they had also licensed code to. Stallman essentially wanted Symbolics to give their code for free to their competitor, LMI, which would have been illegal according the licensing agreement (that MIT wrote) and would have resulted in Symbolics being shut down.
By the way, the comment thread on that blog ends up being about the origin of Emacs and is quite fascinating. Stallman isn't technically the creator of Emacs (Guy Steele and David Moon are), although he did so much to improve it that he is generally given credit for it.
[1] http://web.archive.org/web/20110719154038/http://danweinreb....