Not okay.
Though you might derive some personal satisfaction, you would likely also be reducing engagement from your users in the process.
Seeing only perfect academic rigor in the language of all the other posts may intimidate some who don’t want to risk seeming foolish in front of their peers.
Should they work up the nerve to post at all, seeing obvious corrections applied to what they post would only compound those insecurities.
For others, unsolicited corrections might trigger irritation, or at the very least raise difficult questions of confidence; that what will be later attributed to them is what they actually wrote.