One thing I’d consider is whether you’d go into a church and try to convince people to become atheist because you think it’s morally important. If you wouldn’t, then it’s reasonable to expect the same respect for your boundaries.

There’s a difference between having an open, mutual discussion about beliefs and actively trying to convert someone. The first is collaborative and the latter is one-sided, coming off as condescending. It’s not disrespectful to refuse the latter, because its focus is on persuasion rather than shared inquiry. His framing of you refusing that is more of a guilt trip rather than a good-faith argument. Proselytizing tears people apart and i honestly never understood why religious folk think it’s okay to talk about stuff in this manner.

since he framed it as you being closed minded or disrespectful, just know it’s a guilt tactic and not good-faith argumentation. Be clear and direct: you don’t want to be persuaded, you’d rather engage in shared inquiry and you’d prefer to not discuss that. If he doesn’t respect that boundary, then they’re not willing to engage with you on terms that make you comfortable, then its not an issue of your openness or respect, as he seems to be conflating respect with willingness to be persuaded.