It's just a request which means you have every right to not agree to it. You can like a page but it doesn't mean they see your feed, so it's just a matter of promotion on their part only. I've done it for work purposes before, to promote something someone else has worked on, and it's a good way for companies to market themselves these days.

I think it's going to happen more and more. If you're not comfortable with it, don't do it. I told my boss, my profile pic has me in purple and black tights with pretty goth make-up on (think black lips) but she loved it, coz it showed 'diversity' on the page lol.