They may be harmless, but they're all Black Widows to me. Just like snakes...to me they are all cobra's.
My Brother who taught biology for over 40 years told me that all spiders are venomous. Maybe there is an exception but that is basically what he said.
The good news is most of them are not harmful to humans and most of those whose venom is harmful, have no way of injecting it. For instance the daddy longlegs has very toxic venom but it can’t get it’s venom into humans.