legopig: Boycotting steam achieves nothing. Millions and millions use it, Valve do not care if 0.00000001% of PC gamers boycott them. All companies exist to part you from your money, having 'allegiances' to any is bizarre.
Where to Start
Hard figures are difficult to obtain but about 8% of gamers prefer to use GoG over Steam. We all have our reasons, but a significant number of people don't want to use Steam. Sure many of that 8% will grudgingly use Steam is there is no other option.
If you think 8% is insignificant, then consider this Linux/Mac users are less than 2% of Steam users but many Devs will cater for them.
Boycotting Steam isn't about trying to change Valve, it about convincing publishers that GoG is a viable addition to release via Steam. Something that has happened and continues to happen.
Some "Allegiances" are bizarre, football teams, fashions lines.
But refusing to Use Steam isn't bizarre. Valve puts restrictions on your games, it locks your licenses to a ever changing subscription, it is the gatekeeper and from my experience not a very ethical one. Now if your are happy with this, then that is your choice.
Yes all companies exist to make money, but we can choose to support companies based on their actions. Valve abused its dominant market position for over a decade, GoG while shifting on a some of it original values continues to offer the best service.