Another perspective on this is if you have some idea what you're doing and play aggressively as human, you are far more likely to win the match. The first few kills are in some ways the most important kills of the game. Say two humans rush out and kill two dretches each without dying. Those two now have enough cash for light armour and lasgun which is enough to raid the alien base, and the aliens have no evo, already they start to get stuck in the cycle of being outclassed by the human equipment, and you can push that advantage to the end of the game. Sure a dretch can do 94 points with a headshot, but a dretch dies in 1 shot from a shotgun, or 3 from a lasgun.
Attacking the overmind early means that dretches will rush to defend, leaving your builders alone to build in peace - and as long as you keep killing dretches, they can't evolve.
In this situation, even if you DON'T know what you are doing, if you see a human out getting lots of kills, after they die or come back for ammo, GO WITH THEM on their next run, because if you are not building while they are keeping the aliens busy, you contribute nothing by camping in the human base. Sure you will probably die at some stage, but you will probably have enough cash that you can buy better gear and kill many more dretches than the kills you give away.
Apart from being more likely to win, it is also a lot more fun to play this way. There is nothing like running out of ammo half way back from a base raid as youre chased across the map by a marauder and a swarm of dretches, then just scraping into the base with no stamina, no ammo, no helmet and 2HP as the turrets open fire. For me that is what playing as human is all about.
So yeah, I'm not saying you should never camp, there are times you have to, as this thread points out. But the start of the game isnt always one of those times, and it does seem stupid to camp in the times when there is no reason for it.