You'd be depriving yourself of a huge audience if you make your games steam-only. 
I'm no Steam apologist (and I
do consider Steam DRM), but I would argue that the potential audience loss versus the potential audience exposure would entirely negate (perhaps many times over) the benefits of
not using Steam. Like it or not, and I myself lean towards the not, Steam is the
only realistic choice when it comes to commercial PC games. But by all means try and go through GOG and other DRM-free options, as well as using Steam, for those who wish to purchase games in this manner.
Wanting to provide a DRM-free option doesn't have to mean avoiding Steam altogether.