I don't see the issue here.

Would we be so hard on him if he was knowledgeable about blood testing and had tweeted about Theranos when they ultimately failed?

The less silence is the norm, the better.

We need people to publicly call out bullshit when they see it (at least he waited until they failed rather than when they were trying to succeed)

Some people who thought they knew better than actual experts failed and took 174m of somebody else's money with them.

It benefits certain angels & early stage VCs to have a culture of relentless optimism and fantasy in the face of reality, and to ensure silence is forced on everyone except those who succeed.