For what? Surely it is legal to have an opinion about stocks?

For securities fraud. If he was (as it seems there is some evidence to show) selling at the same time he was boosting a stock, he wasn't expressing a sincerely held opinion. He was executing a pump and dump.

I mean, yes, it's possible the guy simply timed this perfectly, promoted a stock based on an understanding that was technically incorrect but genuinely held, and did nothing wrong. But nine times in ten, that's not how it works. The incentives to cheat in this space are, obviously, huge. And that's why we have an SEC with law enforcement powers.

I remain amazed at the amount of credence WSB is giving this fundamentally anonymous yahoo on the internet. You'll at least grant that there are people who want to scam you in the same way that this guy did, right?