Turkey joining the EU is decades away if it will even happen at all.
If Turkey is a condition to leaving, we can leave if they join. So nothing to be frightened about in advance of something that is unlikely to happen in the short term.
People moan about immigration but our foreign policy has been the cause of it. Do I trust our governments more than the EU? No not really.
We can choose to leave at anytime in the future, but it will be a lot harder to rejoin.