Firing ports are pretty much useless. If the vehicle is moving, hand held weapons won’t be accurate. If the vehicle is stationary, it is a conspicuous target that doesn’t have enough armor to protect the people inside.
I disagree. If the choice is sitting in a cramped lightly armored can with no way of fighting back or having at least a small port to fire my personal weapon out to at least make some noise, I'll pick the latter. Conversely, if I'm some hero with a LAW or an RPG who wants to take out an armored personnel carrier, I'd really have to screw up my nerve to attack something with dozens of small arms pointed my way.
Remember the lessons of the Soviets versus the Porsche Elefant: lots of people swarming an armored vehicle with no close-in protection end up being static displays at the enemy's museums.