It's not the sights. Imagine a situation where you must fire from the hip close in.
Your attacker is upon you. You reach out with your weak hand to keep the foe away while drawing your weapon.
This would require you to keep the weapon close near your hip. If you fire with a ported barrel from this position hot gas and lead shards come straight up into your face. My brother had a S&W model 66 custom shop revo with a ported barrel. If you held a piece of paper over the top and fired it it would shred the paper. We held a piece of cardboard over it and several small pieces of lead lodged in it. Enough to blind you. Ported barrels should only be fired from an arm extended position and this eliminates a few key self defense stances.