I'm thinking of backing out of a trip that depends on me, is that wrong?
It might not be if there is some way you could change your schedule around so you have an excuse not to go.
What you're asking me to do is be manipulative.
I'm just asking you to come up with a reason so your friends don't get mad. There's nothing wrong with changing your mind about going on a trip you said you were going to go on, but sometimes people get upset about these things. I just wanted you to have a good excuse!
I'm thinking of backing out because of a church function.
It's not wrong to change your mind, but if you feel that telling them about it is more transparent you should do that, they will understand if they are real friends.