I understand why a lot of people have a problem with Steam. It is because Steam's a giant, and it's getting bigger all the time. Consumers in this day and age are for the most part, wary of giant money making machines because it makes them feel like they don't matter; that all this giant machine wants to do is eat their money, belch out a cost-effective product, and leave the consumer with no recourse should the product fail to perform. That's the state of modern PC gaming.
I think the biggest problem people have with Steam is that they want to get unlimited value out of their games, and Steam threatens that perceived value. When we buy a game we want to be able to play it forever. And we have every right to expect that. Whoever created the game and owns the rights to it doesn't matter, there are NO built in expiry dates to the software licenses you purchase.
When you sell a license to someone else enabling them to download a copy of some software and use it, then unless the User Agreement specifically states that the license will expire within a certain timeframe, that license is assumed to be permanent. The software might not be supported indefinately, but the licensee still has the right to retain and use the software indefinately within the bounds of the User Agreement.
If Valve should suddenly go belly-up and Steam is no longer functioning (providing updates, supporting multiplayer, tracking achievements, etc.), then a lot of people will be out a lot of money because they can no longer access games that require Steam to function fully, if at all.
That said, I think it's extremely unlikely that Valve will go bankrupt or disappear in the foreseeable future, but you see my point. Having all these games under one roof creates a huge dependancy on that ONE system, and if it should permanently fail, we're all screwed out of potentially hundreds of dollars (individually speaking).
The other side of the problem is that it is only in a company's best interest to maintain a license agreement as long as the property the license is linked to is profitable; but Valve doesn't actually own the rights to the majority of the games it supports, it's just a middleman that happens to control the method of distribution. If Valve decides Steam is no longer profitable and shuts it down, do you think they will compensate all the millions of gamers who bought games through Steam and rely on it to support and provide functionality to their games? Not a chance in hell.
I do have a small library of games on Steam, and it will remain as small as possible. I have bit the bullet and bought some games through Steam that I really wanted to play, and had no choice but to go through Steam to own, like Serious Sam 3 and Worms Reloaded. I'll definately buy Rebellion without question. My love for Sins transcends my distrust of Steam.
But heaven help Valve on that day when Steam shuts down and I can't play Rebellion anymore. There will be blood and fire.