What is your point about collateral damage?

Rounds hitting other people, other vehicles, etc. What goes up must come down, this is an uncompromising fact.

They are susceptible to damage from small arms fire

Penetrative force from a bullet goes down at distance, and when competing directly against gravity and drag that becomes even harder. Try shooting a titanium sheet at 2500 feet with assorted pistol rounds. You will do no damage, assuming you can even hit it; titanium is still titanium.

Catsfive corrected me, I made an assumption about the exterior plating being made from titanium as well and that seems to be incorrect. My bad on that.

I conceded that a .50 BMG round could probably deal significant damage, but would you immediately eject from it within your own borders? Why would gunfire be your first expectation within the boundaries of your own country? That alone doesn't really smell great to me.