We do not usually call a statement »valid« or »fallacious«. A statement is true or false. An argument on the other hand is valid, if it complies with the rules of logic. But this is not enough: »All humans are stupid. Fred is a human. Therefore Fred is stupid.« is a valid argument. But we might doubt the premise that all humans are stupid. If an argument is valid and its premises are true, we call the argument sound.
Note that a sound argument does not require the premises to be proven. This is in fact often impossible. Instead they should be plausible. But deciding on the plausibility of a premise is often subjective. That's where (informal) fallacies come in. They are rhetorical devices employed to make a premise sound plausible. Therefore they are problematic. But the argument itself can still be valid or even perfectly sound. Even the conclusion can be true. Fallacies are just a warning sign that you should double check the premises.