I'm with you in spirit, my friend.
BTW, the carbide tooth saws used by fire departments (I tried to get some when I was running our small VFD, but when a chain costs more than a small saw, they balk) are designed to handle composition roofing, nails, etc. They'd have no problem with the super thin sheetmetal in a lot of residential entry doors.
I'd like to have entry doors with real steel in them. If you're experimenting, don't forget your arithmetic. Alloys vary, but use 0.283 lbs. per cubic inch and you won't be too far off. So a 1/8" plate inside a 36 x 82 inch entry door will add 104.4 lbs. A 1/4" sheet adds almost 209 lbs. But if it was something like T-1 steel, it might be worth the extra framing, hinges and effort.
Just remember, while you're busy designing the super door with metal armor, locking lugs all around like a safe door, etc., that it's a felony to harden your home so the cops have trouble breaking in. In most states, it has to be a drug raid and they actually have to find something (oops! a joint fell out of that last cop's pocket). In a few states, it only has to be a "drug raid," even if they hit the wrong address, find nothing, etc. I have a friend here in WA state who was in prison with a guy doing more time for hardening his home than for the drugs.
Frankly, I believe a GOOD lawyer could make a pretty good case for the defender in a situation where there was clearly no identification of the attackers before they hit the place. But a lot of lawyers can be scared off by cops and government agencies. I've seen it happen. Unless you're worth at least ten million, I think if you defend yourself effectively against cops you're screwed.
“The police of a State should never be stronger or better armed than the citizenry. An armed citizenry, willing to fight is the foundation of civil freedom.” Heinlein