"The gestation period of some species of opossum being seven months, the right of the people to speak freely shall not be infringed."
Even if there isn't a species of opossum that gestates for seven months, free speech might still be a good idea. Or it might not. Either way, the first statement's truth value doesn't change the command.
Now, to be fair: Compared to the founding fathers, we know much more about pretty much everything. I don't really care what they thought was best. I care about what is best for society. If that means more restrictions on guns, ok. If that means fewer restrictions on guns, ok. If it means some other thing, great. Deferring to previous generations makes no sense. We don't do that for disciplines such as math, biology, chemistry, or engineering. Why should we do it for law?