Earlier quoted context omitted.
Nobody is silencing any research, unless you think broadly circulating a memo at a tech company constitutes "research". It is legal to research pornography, but try to view it at a lot of companies in the office. Context is important. He sent it out at work, not to arxiv.org.
It's not silencing research, but silencing talking about research is a chilling effect. This research isn't off-topic pornography, it was research specifically on the topic of who works in the office.
Consider the alternative: say his goal had actually been to learn what most scientists believe or to see how it applied to Google. That would be things like a representative literature survey, lots of questions about how you could measure effects, what the implications those effects would have, etc. Rather than just assuming current staffing was the optimal outcome, you’d ask how you’d even measure such a thing, etc.
Remember, before he joined Google he has experience working in a real research lab. There’s no way he doesn’t know what scientific discussion looks like – it just wasn’t as important as trying to portray his personal political beliefs as objective truth.