Agreed, at early stages in the game, and even in later stages most times, Dretchs SHOULD NEVER attack a base full of humans. Why? Turrets will rip you up and all you will be doing is feeding the human team.
To "attack" with a dretch, you should attempt to lure humans out of thier base (such as, letting them know your out there), and ambush them outside of thier base. NEVER ATTACK A GROUP OF HUMANS BY YOURSELF AS A DRETCH! You can try and pass through, but if your by yourself as a dretch, the odds are against you and you will die when you attack a group alone, especially if freindly fire is off.
In early games, the ONLY time its wise to attack a human base if someone sees them moving the reactor, and as such, their turrets are down. Then, with a group, it might be a good idea to jump in and feed off their spwans.
If you can effectivly attack a human base as a dretch, then you dont need to be reading this thread. Its also a situation where you have to know the map. Some human bases (such as the default Karith one) are more "suitable" for dropping in on a dretch if your with a bigger group of other aliens than other maps.