Well see there, that's where you know you need to stay away from people like that.
When they bring in "converting".
It's one thing to help someone experience part of one's religion ( or lack there of) if there is curiosity. It's another when you're trying to shove beliefs down someone's throat.
Intentions be damned, it's rude. I don't care if someone means even the nicest of intentions. If they can't respect where I stand and are constantly trying to "convert" me, I'm outta there.
Funny thing, I'm Catholic. But I just don't care all that much about what other people believe in. I respect people's stands. THAT, and I got my own stuff to worry about.
As @Mangocado said -- you gotta distance yourself from people like that, who are often extremists. Generally, the average person might not agree, but they'll respect your stand and move on.
As long as you yourself aren't shoving athesitsm down someone's throat -- objectively, no, you are NOT a bad person just because of your belief.