Such an annoying site
I'm house hunting at the moment and I can't help checking places out on this map. It has put me off streets and/or areas, even though I know that the data may be questionable. It's hard not to let it influence your vision of a neighbourhood if you don't already know a place well. I guess that's just how humans work. We can't know everything from first hand experience, so we readily accept second hand information and build it into our world view. The fact of the matter is that the cost of being careful feels low compared the the potential cost of being wrong.
In this case, the cost of turning away from considering properties in a certain street is lower than the cost of moving into a street that does turn out to be dangerous. That's because the cost of not looking at the street is probably only financial (maybe missing a bargain), but will never be known anyway, whereas the cost of living in a street where you get mugged or burgled could be very high because once you live there, quality of life comes into play.
As a buyer, I use this site to rule out looking at certain properties, based on what the site suggests the street would be like to live in.
If I was selling a house on a nice street, that showed as iffy on the website, I think I'd be justifiably miffed.