Now, I'm willing to change my view if there's ever a situation in which Gabe Newall is intentionally trying to avoid paying taxes, but that hasn't happened yet.
What about exploiting child gambling? Valve's value, and thusly Gabe's value, skyrocketed after introducing lootboxes to TF2, CSGO, DOTA2, etc. He can be as charitable as he fucking wants, but he still defends lootboxes while taking little to no efforts to ensure that children aren't gambling on his platform. He's had... how many years to fix this problem now? Too many. He's not fixed the problem, and continues to reap the rewards in the meantime.
As far as I'm concerned, he's just as much of a piece of shit as any other billionaire. The only difference is that he makes toys that a lot of us really, really like; toys that we apparently like so much so that we're willing to handwave child gambling as long as it doesn't get in the way of making it moderately convenient to download DRM-infested games.