All of those are protected speech.
Ok, but it's ok for gun controls to discriminate against mentally ill people, in the interest of public safety, even though it's obviously unfair to discriminate against people for something they can't help.

Here you're suggesting gun laws shouldn't discriminate against people who choose to post "ominous shit", which I admit is a phrase I really like, even though this is a conscious choice and can be a caveat of gun control laws... ie, warn people that if they post "ominous shit" (and perhaps they should define this legally), then they lose their guns. Why is that any different to "if you go crazy, you lose your guns" or "if you go blind, you lose your driving license", or "if you lose control of your bladder, you can't sleep in my bed"?