I do not think that anyone's ability to write should disbar them from discussion. We can not expect perfection from others. Instead we should try to understand them as human beings, and interpret them with generosity and kindness.
You are completely right, but on the other hand if you are going to invoke "science" and you present your writing as scientific (he did), you have a higher bar. If you fail to be objective (see semi-related assertions about Marxism), or your writing obscures the point you are attempting to make, then you've failed as a writer of scientific content.
If your writing isn't good enough, then don't release a memo to your workplace of tens of thousands of smart and ideological people. Put it on a blog, write it anonymously, but expect whatever criticism you get.
Your criticism is that he shouldn't have released a poorly-written memo to an enormous company. I would agree, however, I don't think that's what happened. I thought he brought it up in the internal Google Skeptics group, and then it got leaked and went viral. I doubt he wanted such an enormous audience for this draft, but I'm open to hearing statements to the contrary.
"Shouldn't have shared his opinion" and "should have shared his opinion in a different way" are two completely different things, and I don't see many people saying the first.