First of all, a random online comment is not protected by copyright law afaik.

You got a fundamental aspect of copyright law wrong right in the first line.

Your comments are indeed protected by copyright.

Secondly, if you did take something protected by copyright and then used it for commercial purposes

That's wrong too. Whether or not someone's making money off of a copyright violation will affect the damages you can sue them for, but it's copyright violation either way.

Also copyright is not about just copying but also distributing as well. Playing.(radio) songs in your coffee shop for clients is treated differently than you listening to it at home.

Technically true, but what does it have to do with these circumstances?

You generally can't just profit off someone else's work without them allowing it.

Generally speaking, sure you can. Why couldn't you? People do work that other people profit off of all the time. If a carpenter builds a desk and then I go sit at it while doing my job and earning millions of dollars, I don't need to ask the carpenter's permission.

Copyright has a few extra limitations, but those limitations are on copying stuff without permission.