That's correct, article 5 doesn't actually stipulate that members must engage militarily. Each country can decide on its level of support independently. However, what matters is perception. Currently, western public believes that article 5 is an ironclad guarantee that NATO members will be collectively defended. If a NATO member is left to hang, then it becomes clear that being a member of NATO doesn't actually provide any meaningful protection. At that point NATO is exposed as the protection racket that it is.