I didn't read all the replies (I assume this will be a turbulent (haha) thread) but personally, I believe that if the seats are able to recline, then whoever is in it has the complete right to recline it all the way regardless of who is behind said person. If it is allowed, it is allowed. I would never ask someone if it was okay to recline because, quite frankly, (as above), if it's allowed, it's allowed.
I don't personally get annoyed even though I'm a tall girl and my legs do get squished/can't keep my tray down unless I uncross my legs (and even then it barely lays flat etc.) but that's just budget air travel (and I am so cheap so I'm never upgrading lol, perpetually smushed legs for the win!!).
I don't usually recline at all (unless an overnight flight and I'm attempting sleep) because I know it does inconvenience the person behind you but I would never ask or not do it if I had a reason or want to.
Airlines honestly should probably just take the recline away. It only reclines like 7-8 inches anyway, it's barely a slant, but everyone hates to be the "reclinee". Just remove the problem by taking away the privilege for everyone (or just the cheapies).