I'm thinking of canceling a trip away with my friends.
Is there a reason that you think you should call it off?
Yes, I think that trip would ruin our friendship since we don't think alike and we've been together for so long.
Canceling plans that you have made with friends is rude unless you have a valid and pressing excuse not to go. You should spend time with your friends, especially since you have been together so long, as long-lasting friendships are hard to come by and should be valued. Rather than think the worst about your trip, be more optimistic and appreciative of the opportunity to spend time with your friends.
It was an excuse to get out of the trip, I didn't want to go the whole time.
I think that you should have told them that in the first place. I think that it will really hurt their feelings if you decide to back out of these plans now, especially so last minute.