Why do you say them: 邪教? It is your fault.

I don't trust 摩門教, but you are too rude to tell them it is 邪教. If someone said what you trust is evil, how could you think?

You can tell them you are not interested in it and you are busy. It is fine. However, since you said them 邪教, they will keep to explain you they are not 邪教.

I think you should make apologize to them. Also, tell them you are busy and you don't want to join in them.