Urban Decay is what happens when cities start letting small offenses slide. Not enforcing small offenses leads to bigger offenses, and so on... This can have disastrous results in a short amount of time. You notice it under highway bridges in cities all the time. A once quiet place can turn into a 3rd world slum in just weeks:  

At first there's an empty bridge area:

 

It starts innocently with one person:

 

No one tells him to move, so he starts chillin:

 

Still no one is telling him to move, so he starts to get more comfortable:

 

Welp...no one has told him to go away, so he starts setting up a structure and smokin' up:

 

Another dude sees this as a consequence-free place to camp, so he decides to join:

 

Well clearly the cops aren't doing anything, so more people join and it becomes a party hangout:

 

Put a lot of drugs, weirdos, and zero laws together, and things eventually get really scary:

 

In a short amount of time, normal people no longer feel safe to use this area:

 

What was once public property, has now been taken over. People start to avoid the area and the local economy goes down:

 

Enabling people to live in these environments starts to destroy them beyond repair:

This can all be prevented by allowing the police to enforce very simple laws:

  Crime will always happen, but it can be contained by enforcing strict but fair rules. You will never prevent ALL homelessness. You will never prevent ALL murder. You will never prevent ALL theft. You will never prevent ALL greed. But by enforcing small laws you can prevent the problem from getting larger.     90% of more of homeless people are not the problem. It is under 10% of that population that refuses services, is not trying to better their situation, and is unfairly taking advantage of the the generosity of the population. No, it is not your right to get a free pass from rules. No, it is not your right to live and take over a public space. No, it is not your right to be able to litter and destroy a public space. No, it is not your right to be provided free unlimited housing by the city. Yes, you should have to follow the same rules as everyone else. Yes, you should be forced to accept services or arrest by not following the rules.