There are two discussions:
1) What is the law (which doesnt care much about original intent anyway)
2) What the law should be.
As for #1 the law is quite clear “Shall not be infringed”, and any talk of militia has long since debunked a it is an exemplary clause not a conditional clause (we can verify that not just with early court documents and statements from the authors, but also its obvious from the wording if you replace it with similar sentence structure to eliminate your bias, we can discuss that separately if need be).
As for #2 that matters even less about original intent and has everything to do with what is the right choice… The logic is quite simple IMO If someone is about to kill you almost 100% of the time you will be killed and the murderer gone long long before police arive. ITs the nature of it. In fact in almost all cases you wont even be able to call the police until after the crime (in other words once your dead or dying).
Your only possibility for survival in such a situation rests solely on you, I for one find it irresponsible of anyone who is not armed for this very reason.
Keep in mind we arent just talking about humans here, the logic applies equally to wild animals (for example I always take my gun hiking and camping).
Thats the biggest logical reason, I have many others, and yes as a check against tyranny and invasion is a very valid one too. But overall they are much less relevant arguments.