What’s the deal with excessive drug addiction in major North American cities?

[ana]

I've seen videos of some cities in North America showing areas completely overrun by drug addicts; it looks like a zombie apocalypse.

How can the inhabitants and authorities of these cities remain indifferent to so much human degradation? Do so-called normal people find this normal?
There are drug addicts in Europe too, but I've never seen anything like it in my life before...

Is your city also affected by this problem?