While it is possible to split a fitting or valve by tightening too much, it is not common unless you are using a really long wrench or it is defective in the first place. Pipe threads are tapered and interference. The tighter you turn, the more it wedges itself into the fitting. The tape or pipe dope seals around the threads to make it waterproof, the tapered function holds it together. Some people use the belt and suspender solution of putting some pipe dope on top of the tape. You might try that. Either one should work on its own, though.