There are a few issues with Steam. One is privacy - you literally sign your rights to any information you give them away, meaning they can mine your computer system for info, as well as your account, sign up details, email etc and sell or supply them to third parties - they do have a disclosure agreement you can look up to see what you're agreeing to though. Another is the steam client hooks into your operating system to run anti-cheat / DRM stuff so the software is a lot more invasive then your regular amazon software store, its more similar to an antivirus program.
I run steam games but I have a modified DLL to do so because I don't like those sorts of programs on my computers. When I close my game I don't want it to continue running on my system or updating itself automatically when I login without asking my permission.
Lastly there is some controversy over the valve anti-cheat system. VAC is an automatic cheat detection system (see above). If you are banned by the automated system you can lose access to your steam games. The problem is Valve will not discuss the VAC ban with you and you are banned for 3 months, not only on your account but all accounts linked to your phone number - if your kid downloads a cheat from the internet and the VAC detects it, bye bye kids account, your account and all accounts connected to that phone number, and all the games you've purchased.
I say screw that, I don't use steam but if I did I'd be immediately banned most likely. Seems a bit over the top to me.