Wrong. That's not what pipe dope is for.
Yes, that would be the problem -- combined with not understanding what pipe dope is for. Pipe dope is *not* a sealant to prevent leaks. It's a *lubricant* that makes it easier to tighten the joints enough that they won't leak. Pipe threads are tapered: the pipe needs to be threaded far enough into the fitting that the tapered threads expand the fitting slightly. *That* is what keeps the joint from leaking.
Same reason.
And now you know.