I can't imagine a single judge in this country would condone the use of an SMG or SBS as a defensive weapon and you would likely be guilty the moment you walked into the courtroom.
Any judge that thinks that shouldn't be on the bench. If the act of self-defense is justified, the tool used is of little legal importance. That you fired nine 9mm projectiles with one pull of the trigger, vs. fired nine 9mm projectiles with one pull of the trigger, is a non-difference (that's 00 buckshot from a standard shotgun vs. a long burst from a SMG). That you fired shot from an 18.5" barrel vs. a 14.5" barrel also makes no practical legal difference.
The only reason you'll get scrutinized more is that NFA weapons have been demonized, and a smart judge & prosecutor will only press the case to make sure the tools involved were legal. Any that do deem you "guilty the moment you walked into the courtroom" are grossly negligent in their sworn duties.
The prosecution's arguement will be simple and effective; you used a weapon designed for full on combat and therefore were looking for trouble.
Defense's argument is also simple: if I need to exercise deadly force on someone who broke into my home and behaved in a manner threatening my life to a degree that I actually needed to risk killing him, I wanted to make sure I would be the one standing in the courtroom defending my actions, not assuming room temperature - yes indeed it was full on combat. As for "looking for trouble", it was my home and my life - I was NOT unlawfully in someone else's home violating a host of laws and threatening lives.
A suppressor is of no tactical significance
Go fire a .223 round indoors sans earplugs, and get back to us on the "tactical significance".
a good shoot is a good shoot, a bad shoot is a bad shoot.
Bingo. The tool only helps either be more of what it is.
My machine guns would be the last guns I'd go to. They're strictly toys.
Which is why the military & police use them, right?
full-auto may result in larger legal bills.
This is true. I'd rather be paying larger legal bills than increasing my odds of being dead.
Hearing damage is usually caused by prolonged exposure to loud noise. Are you planning on shooting someone in your house on a daily or weekly basis?
As above: fire a single .223 round indoors sans earplugs, then get back to us.
I was too close to the wrong end of a .308 without earplugs once. A single shot messed up my left ear's high frequency perception permanently. It only takes once to cause permanent damage.
in my area, using a NFA item for home defense and conceal carry is not smart, actually its stupid.
Depends on the jurisdiction. Some forbid it, some frown on it, some are happy you won the fight.
I shot my handgun in my home w/o hearing protection and I did not hear the shot nor did my wife.
Psychological processing of the auditory information is different from the physical impact on delicate hearing components (and the latter have a mysterious ability to
sometimes put up with extereme noise without damage, but that's not assured).
when I say suppressed I mean a suppressed pistol.
Then say so. My HD gun will soon be a suppressed rifle.
A suppressed pistol on the street will get greater scrutiny, as it falls into a category that, under current social norms, practically cannot be used that way. Nobody is going to carry an M16 around daily for SD, nor are they likely to carry a suppressed pistol - both are simply too long for convenience.
There is no law (your jurisdictional mileage may vary) prohibiting NFA use for self defense. The only problem is it may create circumstantial issues that will take time & money to deal with in court. So long as it's a good shoot you should be fine - evil prosecutors aside.
Regardless of tool used: if you shoot someone, expect arrest and prosecution. NFA items will increase those odds, so it better be a good shoot.