Can you criticize something even though you have no area of expertise in the profession?

Yes, it is okay.

It would be wrong if you were to criticize the methods.

If you were to say you don't like they way a singer sings because of how they were taught, despite never having taken a single lesson in your life, that would be considered ignorance.
To say you don't like the way they sing is just a superficial preference, which everyone has the right to express.

lol silly lug of course you can that's how trolling was invented :3

Yes, I can and do.

Most of the time, no, I can't. There are exceptions though.