I don't think it's really the place to discuss about illegal file sharing. There could always be a debate on its statistics, its causes, its consequences, etc. But throwing a tantrum against those who don't pay their games and
in fine don't use Steam is by definition out of topic. If the goal is to hide the problems of Steam in the name of the holy crusade against baby-eating pirates*, that's a very low move and should be condemned.
About the argument that Steam runs without problem in the background : it sounds like you're not listening to players who have problems. Steam running fine in the background becomes an awesome feature when it's the minimum we can ask from it.
There are technical problems with Steam that you can't deny. You can compare it to gamestopping DRMs to feel better, but there are still important problems with Steam at game launch. Obviously it modifies the process, causing protections against process modification (virus, keyloggers...) to freeze the launch. Also it means that it can alter the stability of the game itself. You could see the difference with the pre-patch executable. The simple modification from Steam caused a lot of issues, proof that Steam isn't a clean DRM (if that exists).
If you like Steam that's great, you don't see any problem. Cool. But you have problems with it while not necessarily appreciating what it adds, it looks like an unwanted sacrifice. I think nobody wants Steam user any sort of curse on their family or whatever... we just ask the choice not to use it. There's a moment you have to rely on the serial number as an identification to allow support on a product. If you want customers to use your application, give them incentives, not threats. And that's what's wrong with Steam for me. It's too aggressive. They take the monopoly by force and then throw their price policies at the face of the customers. That's not how business should work, even in a capitalistic world.
Just the "$ = €" conversion is insulting. They aren't the only ones to do that, but that doesn't justify it. And as they are suffocating retailers by forcing people to use their plateform to play, it's plainly dishonest.
I'm for the choice. You like pseudo-achievements, community things to share, easiness to buy and get your games, accessibility to your game from anywhere that has a decent internet connection? Perfect, use Steam. Just don't force me to use it when I don't want. I'd like that Steam would make efforts to convince me to use their plateform rather than imposing themselves, letting retailers with only console games to sell.
Spoiler * : I'm against the use of Piracy and Theft for the illegal file sharing and illegal downloading of copyrighted content. Particularily when there are still pirates and victims of pirates nowadays (Somalia, Indonesia...). Piracy is about pillage, murder, torture, extortion, theft, destruction of properties, etc. It's not the glamorous picture hollywood likes to give. I know this abuse of language has been accepted even by jurists.
Also it technically isn't a theft, as nobody loses its property. Let's be precise, it's a counterfeit, which is more important than a theft.