I don't think a correction is necessary. Both parts of the sentence are already in the present tense. Plus, the use of "us" in the beginning of the sentence indicates a personal attachment.
Hamlet feels that is where a woman has a best chance at being faithful, and where she will cause the least amount of damage. After all, as he tells Ophelia also, "why wouldst thou be a breeder of sinners?"; in a nunnery, she won't have children and bear wicked men-like his uncle-that do awful things.
