While most shelters wont let someone who is drunk in, there are also many many shelters that are under funded and cannot remain open 7 days a week or have limited space and not everyone gets a bed.
Some shelters even require a small amount of money from the homeless person (I prefer that term over bum) to let them sleep, so if the place is packed, they will sometimes sort who gets in and who doesn't based on who paid.
They do the best they can with what they have, and will always try their best not to turn people away, but its not always the homeless person's fault for being on the street.
That being said, I do like your image. Makes a nice statement of today's unfortunate society.
I think I would of preferred a black and white version and maybe crop it down a bit to remove some dead space on the upper left hand side