How can you be so confident that the thief was not armed? Despite all of the anti-gun legislation in Great Britain, there are still plenty of gun crimes. The only people who you can guarantee are not armed are the lawful ones. And law abiding citizens are the ones you don't need to worry about in the first place.
I don't see myself as being part of the problem so long as I'm passive and do not initiate anything. Your reasoning is like saying that because I have car insurance I'm causing automobile accidents. Being prepared for something is not the same as perpetuating it.
What's to say you won't end up dead anyway? If you want to take the chance that a violent criminal will just take what he came for and not hurt you, that's your choice. Me? I prefer to prepare myself for the worst case scenario, then live happily ever after if it doesn't come to pass.
You are right, to a point. The Weimar government passed legislation against owning weapons, and that legislation affected everyone, not just Jews. This was done to prevent violence (which it did not accomplish) and prevent extremist takeover (again, not accomplished). Once the Nazis took power, the law was amended specifically to prevent Jews from owning firearms.
Now, this is not to say that had they been armed, they would have been able to resist Nazi oppression. Few Jews owned firearms, even before the legislation was enacted in 1928. However, it's quite obvious that unarmed civilians have very little chance against an armed military, while armed civilians at least have a fighting chance.