Whether to tell his prospective employer that a new male post doc opposes affirmative action for women in academia? I personally know a male graduate student who works in a different area (in STEM) than mine and who has a potentially controversial view.  He opposes to affirmative actions for women in academia and outreach activities for female teenagers conducted by a university.  He's repeatedly and openly expressed his idea on his public Facebook post, in his (and my) native language, which is not English.

This particular student is soon graduating and has been granted a post as a post-doc at a very prestigious university in the U.S., from (I suppose) this fall on.  I don't think that whoever in charge of hiring him knows his view, since, albeit they are public, his posts are not written in English.

While I don't know if his beliefs should prevent him from being hired, I do think that this may be a potential concern to his future employers.

Obviously I'm really concerned about his views and feel that, since they are expressed openly, it might be appropriate to make sure his prospective employers know about them. Is there a professional way to do this, or is it the case that no matter how baleful and publicly expressed the views may be, I should play no part in informing his prospective employers?

Corrigendum: I should have been really, really careful as to how to put my question.  For one thing, I don't see his view anti-feminist.  The word anti-feminist appears there (with quotation marks) because I couldn't think of a good adjective.  It could have been anything else.  Since so many people are distracted by this, I remove the word completely.
Mind your own business.

If you believe that your colleague poses an actual threat to someone, it is of course your duty to warn them.  But opinions are not threats.  It is entirely up to your colleague who he shares his opinions with.  Revealing your colleague's opinions to his future employer, no matter how offensive you may find them, would be a violation of his privacy.