Shorting a stock because you genuinely believe the company is crap is not market manipulation.
To be clear, market manipulation is very vague and very broad, and from what I've read the SEC is only going after you if there was fraud or lying involved. Most of WSB's activity is not illegal market manipulation.
Trading (or posting) to cause impact and affect other positions you have is manipulation too. But it's not really provable in the case of WSB so they're safe.
It is not market manipulation for short interest to rise above 100%. It doesn't require anything nefarious. No collusion between institutional investors required either.
To be clear, market manipulation is very vague and very broad, and from what I've read the SEC is only going after you if there was fraud or lying involved. Most of WSB's activity is not illegal market manipulation.