Picture this, your in a heated fire fight and one side is out numbered 3 to 1. The out-numbered gang is diligently picking off the grater opposing gang, or whomever, but, the greater opposing gang's numbers are consistently rejuvenated with re-spawned members re-joining the fight. This would leave the out-numbered gang at a horrible disadvantage as they could never gain a foot hold on the situation. The fight would continue until the out-numbered gang's members were all dead, or, they simply gave up the ground.
This is just one reason why when your dead, your out. There should be no returning to the fight. This would include any situation whereby two groups of opposing players were involved in some sort of gun-play. And yes, I know there are rules for different situations regarding this...
Every team is playing based on the skills of each of their members. If the members of a smaller team have better skills than the opposing larger team, the smaller team should, in theory, prevail.
Same goes for gangs of equal numbers. The fire fight should be based on merits, skills, and team work, and not be disadvantaged with dead players spawning in and re-joining the fight.
That said, those of you who have been in these situations already know this, and have most likely experienced this first hand.
My 3 cents