Oh those kids and their shenanigans! Despite what others may think, I actually think these things are cool looking. As I've walked around, I noticed that most of these tagged up doors are on buildings are falling apart from, what we Turks call,
bakimsizliktan (that is, not looking after them). So yeah people may say their destroying property and vandalizing, but what's the point if no one is actually cares enough to do something about it (like fix up these places in Beyoglu, I hear real estate is booming there).
The graffiti in the streets is a good contrast (and also something that is there) to the ornate Ottoman architecture. If I'm gonna take pictures of the pretty doors and the pretty ugly doors, then I gotta take pictures of these as well. It's what's there.
I may add, they got good graffiti in Istanbul.