It's just like all the other requirements needed to play. You can't keep making games for old 3dfx cards.
But its not. Its not like all the other requirements. A game can play perfectly fine without internet connection (unless its a MMO

If Steam wasnt a requirement, but a volunteering way of keeping games updated, a way of socializing, a mod database, a hub for MP'ing and a gameshop with some nice discounts, then I bet everyone would love it.
The fact is that it IS all of the above, but it is being FORCED upon the player, which is why so many hate it.
Does it help against piracy? (which I guess is the reason for having it)
No. I honestly dont think it does.