Gun people insisting that the word "assault rifle" only applies to automatic or select fire rifles (or better yet, doesn't apply to carbines or submachine guns)

Um.. In this example, a rifle is still semi-auto only*. A carbine is >16" barrel while still retaining functionality of a full-sized rifle. And an SMG is similar to a carbine but fires smaller pistol ammunition.

Theoretically, a carbine and/or SMG would in fact still qualify by it's "select fire" rate if they had one. A lot of reproduction firearms are made to look like the military counterpart (like an MP5 or AK-47 can't be legally bought, so they make clones in a semi auto-only). You cannot legally own any firearm that has more than 1 round fired per trigger action (without going through a lot of work to obtain a FFL). Aka you squeeze the trigger and only 1 round is fired. Select-fire would apply to military-grade where you could have select fire to burst or full-auto...

A detachable magazine doesn't define "assault" rifle. In this case being semi-automatic and not bolt-action (where you manually work a lever to unload and reload rounds) but either could still be fed by a detachable magazine or individually for the BA.

But whatever you want to call two-handed firearms with detachable magazines

I would call every pistol a "two-handed firearm with a detachable magazine", because this isn't the movies! You should have one hand gripping while the other hand secures/steadies. Unless you're wounded, uneducated or inexperienced, a thug, or in a movie, I don't recommend 1-handing any of them!

Even if it's technically a carbine or a submachine gun or a pistol with a foregrip.

I don't know of too many people willing to install a foregrip on a pistol, but you do you 😁

Look, calling all of them by a generic name like "assault rifle" is only meant to sound big and scary to everyone who doesn't understand otherwise. So claiming "it's all the same" actually isn't. I wouldn't call a motorcycle a car just because it's motorized and has wheels, same with a bigger van, truck, or RV. I don't think you would either, because you're educated enough and experienced enough you call them by their proper classifications.

Edited missing words