Steam is DRM. And I say that as someone who has been on Steam since 2009 with hundreds of games bought and installed through it. It's fairly innocuous compared to crap like Origin and uPlay, but it's still a layer between you and your games which can prevent you from playing them. They've made playing offline slightly less terrible than it used to be but the possibility of losing access to your games because Valve goes under or goes scumbag, your account gets locked/banned/stolen, &c. exists.
e: IOW I'm not really concerned about short-term consequences. I'm concerned about whether I'll still be able to do whatever I want with the game I bought twenty years down the line.