I don't know what, if anything, was actually forwarded to Zak by Mike. Do you? Does anyone who is indulging in this "resulting anger" you're justifying? Let's be clear--at the time, Zak was coming under fire for being a tool to people online. That's it. Mike was asked to look into it, and my guess is that he said to Zak "you've been accused of doing the following things... do you have an excuse or justification?" Maybe it was apparent to Zak who had complained, based on the nature of the accusations, I don't know.
Mike was never, as far as I can tell, in the position of investigating accusations of domestic abuse, which is what Zak is now in trouble for. I find it difficult to imagine that Mike would be asked or would agree to conduct that kind of enquiry.
So what we've got is a situation where Zak said some crap to and about some people on the internet. Mike was asked to look at the situation and was mostly dismissive. Years later, Zak is accused of domestic abuse, and now people are screaming that Mike should have taken steps to "deplatform" Zak back then, because apparently Mike should have known that someone who was saying crap on the internet was also abusive in real life. People who don't know Zak, his (ex)girlfriend, any of the people who Zak was talking crap to or about, or Mike, are nevertheless feeling all kinds of entitled to their share of the "resulting anger" without any obligation to know what the hell they're talking about.
To be clear--if Zak harassed you and Mike was dismissive of that harassment, you have every right to be angry. If you have done your homework and become knowledgeable about this issue (with respect to actual facts, not just accusations) then you are absolutely entitled to hold and share a strong opinion. But if you're just mad because you haven't seen Mike apologize enough for something you heard he might have done which may have empowered a scumbag to be a bigger scumbag and that's suddenly relevant because you've heard that scumbag has been accused of some horrible (but unrelated) stuff, then it seems to me that you're just joining an outrage mob for the opportunity to vent your spleen on someone without repercussion.