I would never accept a friend request from someone I don't know. Facebook is what you make of it - I view it as a way to keep up to date on people who I don't see or talk to often, and they can keep up with my life. I'm fine with that.

I also add people I interact with on a regular basis who are just aquaintances. I also use facebook to keep up to date on community things - my city has it's own facebook page which keeps up to date on things such as upcoming events, reminders about garbage pickup, updates on water breaks, etc.

There is nothing harmful about facebook if it's being used responsibly really.
Don't add people you don't know.
Don't expect a deeper relationship with someone than you already had.
Don't post things that are inappropriate.
Don't instigate drama through passive-aggressive posts.
Don't focus on it being a popularity tool.
Don't say things that you wouldn't say to everyone in person.
Don't air someone else's dirty laundry.
Don't post pictures that you aren't ok with everyone you know seeing.
Don't engage in trolling behaviors, political/religious debates, etc unless you are able to remain calm, respectful, and not take things personally.
Maintain healthy boundaries.
Use common sense, etc.

Like pretty much everything else in life, it's what you make of it. That's at least how I choose to view it, so I enjoy having facebook.