As a life-long frequenter of Santa Monica's business and tourist districts, I would take exception to this. While there is a significant homeless population in the city, they are IMO more passive then in most places. This is because city services are relatively homeless friendly vs. most jurisdictions. Also since the city recognizes the importance of tourism, they tend to keep the homeless from harassing visitors. "After dark" in a place like the Third Street Promendate shopping district on most nights you will see homeless people, but they are practically invisible since there are so many tourists, local residents, and law enforcement personnel around.

There are parts of Santa Monica that common sense tells you to avoid in the middle of the night (around Olympic or Pico), but overall it is a safe city.