1) Home invasions rarely are perpetrated by a single attacker.
2) An AR-15 is a very simple firearm. It takes minimal training to maintain and use.
3) It is highly effective.
4) It's versatile. A single lower can be combined with multiple different upper configurations for different needs.
5) It's variable. The modular design can make it comfortable and ergonomic for almost anyone.
6) It's reliable. It's simplicity of design provides a platform which is not prone to breakdown.
The fact you even ask the question shows you don't know what you're talking about....
Most say it's for fighting our own government. It's far more likely that NK or Iran will attack our infrastructure. The social collapse that would follow would be a dangerous scenario. If you and your family were facing 3-10 armed and starving intruders, you'd want the kind of power the AR-15 can deliver. The AR platform is not dangerous. The hands it rests in are the deadly component.
I hope I never need to use my weapons (yes, I have more than one AR), but if the time ever comes I'll be glad I have them. In an ideal world, no one would ever need an AR. In that same world, no one would need police either.
There's such an easy proof here of why gun ownership is imperative for a free society.
Senario: You don't like guns and don't think people should have them.
Test: Just take them by force.
Result: You fail.