The Second Amendment guarantees the right to keep arms. When and how you carry outside is a matter that is entirely within the power of a state to regulate.
“When and how you carry outside is a matter that is entirely within the power of a state to regulate.”
Prohibiting the right to keep and bear arms is not a matter for states to regulate just because someone crosses a state line. Other aspects, perhaps, but not that.
To frame it from another angle, extend your argument to freedom of speech or religion and tell me how that would be ok?
“The Second Amendment guarantees the right to keep arms. When and how you carry outside is a matter that is entirely within the power of a state to regulate.”
What you are saying it is entirely proper for one state to prohibit carrying a firearm, and a bordering state to require carrying a firearm.