Rome was a cruel, nasty place.
It was cruel, yes, but better then most places. If you had to live anywhere in the western hemisphere back then, Rome was the place to be. Sanitation, entertainment, jobs, security. Women from all over the globe at prices that could not be beat!
It's been suggested that a good many of the early christians were marginals of society. Untill Constantine became an Xtian there was no guarantee that Christianity would become the major religion it is today.