To try to shed a little light on this phenomenon, the "it" you refer to expands to "why women and minorities may be biologically less qualified for this job, and those that are here as our teammates are illegitimate in some way."

Using the expansion in your paragraph:

=====

I don't understand the attempts at shutting down conversation about why women and minorities may be biologically less qualified for this job, and those that are here as our teammates are illegitimate in some way. If you think he's wrong, you share your opinion and persuade others. You don't shut down the conversation and pretend that women and minorities are biologically as qualified for this job, or that their hires are as legitimate as anyone else's.

=====

That's what some people are hearing. Hopefully it's obvious why management at most companies would consider these discussions to be less than helpful in fostering the most productive work environment.