They don’t realise they wouldn’t have to fear other people so much if there were no guns available in the first place. I’m sure I’ll get a lot of replies that gangsters don’t obey rules and what not but isn’t that the same in every other country without guns?

Home invasions happen in countries that have strict gun laws. I've lived in a bad apartment complex (one apartment was a trap house, a neighbor was stabbed on his way home from work, several vehicles were stolen and mine was vandalized), and a neighbor tried to get into my apartment late one night. I didn't own a gun at the time, but I absolutely would have stabbed him with a kitchen knife if he had broken a window and stuck his hand inside. Instead, I asked him if he was okay and explained that he was at the wrong apartment.

In this case, the person was literally breaking into the house, broken window, reaching for the doorknob. The homeowner had every reason to think their home was being invaded. And given how violent crime can get in the states, unfortunately shooting first in such a situation does make logical sense.

The situation sucks, but this case might be more on the system than the shooter.

You don't need a gun to kill someone, it's creepy enougth to assume the intruder has 'just' a big knife

That type of thing happens in the US as well. It doesn't ALWAYS end with a gun. I'd say most of the time it doesn't.

This person broke a window though and was actively forcing themselves into the home. That's a pretty big difference from "trying a key and ringing the doorbell."

It's always going to be a judgement call, for a different intruder theirs would've been the right call. It's not even about guns, there are knives, drugs, etc. They're all relevant and the kinds of people that are breaking windows can be dangerous.

I forget all the details but a former neighbors son had an extremely traumatic experience when he was out with a trainee as a paramedic and a guy hopped up on some concoction of drugs incapacitated him (I think by throwing him against the wall) and then the dude spun around and beat the trainee's skull in with some object.

Just because you haven't heard of it... doesn't mean it doesn't happen in your country, but I hope you're right. Idealistically you're definitely right, this sort of thing never should happen, but sometimes there's no good answer; you just do the best you can with the information and situation you're in.