It only becomes an Assault Rifle if you have the intent to kill or seriously injury somebody.Also no, a Rifle isn't extreme for home defense. Any gun has the ability to kill, people target rifles becasue they look scary. 

So would you rather live in Wyoming, a state where many people own guns (59.7%), but only 1.4/100,000 people are murdered on average, per year, or in Washington D.C a U.S adminstrative region where guns are essentially illegal (3.6% of people own guns), but 21.8/100,000 people are killed per year on average. 

in germany, thanks - I doubt gun owners throw away their weapon at the state border

I'm sure there are parts of Germany where the homicide rate exceeds parts of the U.S. 

and I'm sure the moon would be utopia in that regard, still not my prefered place to live

I live in one of the western coutries where the guns by capita is very high and we don't have any problem with that. I don't really understand why in USA there so many problems about guns like school shootings etc.

My point was, owning guns does not increase homicide rates inherently, and there are places in the world with low homicide rates and high gun ownership. Your entire fear is based on that of murder. So there are two logical positions you can take when trying to understand why gun ownership doesn't bother some people. Murder by gun is worst than murder by something else, these other people don't believe that. I don't think anybody takes this position, but you can correct me. Higher gun ownership implies higher homicide rate, which is not necessarily true, and that is why I mentioned Wyoming vs. D.C (or practically any liberal state/city state that tries to restrict gun ownership - California, New York, Illinois, etc.) 

and my point was that where nobody lives nobody is killed by guns - Wyoming is pretty much the moon, I know, because I was there and my brother spent a whole year there

it's not that people aren't shooting there, they just have less chance to hit a person

AR-15 and its brethren (whatever you want to call them) hold a number of advantages over handguns or shotguns when it comes to crime potential including larger capacity magazines and intermediate cartridges. The "self defense" potential on the other hand is virtually null, as the main advantages are the ability to do more harm with a single clip as well as increased range.

I think that someone who knows how to use a gun should be just fine with a pistol in most home defense situations

Maybe the problem is not really guns but the relation that americans have with guns. Something about the image of guns in the american culture.