What do you think about correcting peoples' grammar and spelling online, should it be done or not?

Any time I see incorrect spelling and grammar, whether it’s on facebook or Youtube, I immediately correct it, it’s just my nature.
I sometimes will see other people doing the same, correcting incorrect grammar.

But apparently some people don’t like to be corrected and can be downright defensive and hostile in repsonse.
I realize English isn’t everyone’s first language and it’s understandable a few mistakes will slip through.

What’s your take on this, or you don’t care one way or the other? How would you respond if someone corrected your grammar or spelling online?