I'm assuming you're talking about US Copyright law.

Satire isn't protected by Fair Use. Parodies are.

Satire will make a more broad point--in this case, the damaging effects on mental health that social media plays. Any use of copyrighted works won't likely be protected.

Parody would be something smaller--like creating a website that looks similar to Instagram, using humor to criticize it.

It actually can be protected by fair use -- it's ruled on a case-by-case basis: http://www.newseuminstitute.org/first-amendment-center/topic... (scroll to end) You're right in that there is no BLANKET protection, but it has been used for protection before and continues to be.

Don't you have to actually satirize the content being used, though? It would seem that using images to create a satire of something totally separate would require permission.

You're correct, thinking you're allowed to steal anything just because you're going to put it in a content satirizing something else is such a huge misunderstanding of the law.

E.g. you can use melody from a Justin Bieber song to make fun of him/the subject matter of the song, but if you make a video to make fun of Trump and you use Bieber's song as the background music, nope!

You're not likely to get taken to court though, are you? You would expect to receive a cease and desist letter or a DMCA takedown first, right?

If you weren't making any money off it, and it wasn't your intention to make money, and you had no monetisation avenues active, and you only made a handful of infringing media, during a brief period, what's the worst that could happen?

Parody is only protected in the context of copying the thing it is parodying. Beyond that copyright applies.