Condoms don't protect us from everything. So in a probabilistic sense, if instead of just 1 or a few lovers, you have many it's bad in that you're raising the chance of encountering someone with something icky.
Ron Jeremy remarked in an interview despite all the sex partners he had making porn, it wasn't until a non-porn liason he first caught something. So the lesson being I guess if you take precautions as is done in the porn industry you can minimize the risk even sans condoms, but if ya don't watch out. Best advice remains get tested regularly. I do after every relationship and before beginning new ones. If nothing else, piece of mind for myself knowing I'm not passing anyting on is nice. And why would I 'dip my wick' in someone who isn't tested to offer the same comfort?