As wlesieutre mentioned, Team Fortress 2 wasn't free until after microtransactions have been around for some time.
Early on, the game had a consistent 1960s theme and each character had a consistent distinct sillhouette and behavior, so the game was easy to pick up and it was reasonable to play it competitively. It had great game design. Over time they ruined all of that for the sake of profiting off of addicted players.
I really can't muster much support for your indignation.
I can't help but think that the hats actually add to the game, by allowing players to choose a semi-custom look for their character while playing, making a specific character easily identifiable.
Your reasoning make it sound like you're just upset that they took something that you had been accustomed to, and changed it. I note how you didn't mention any stats, or even a hunch as to whether most players liked or disliked the hats.
Additionally, you cast the players as "addicted", and Valve as somehow taking advantage of their addiction. Let's get this straight. The players aren't addicted to TF2 (even if you somehow proved they could be addicted to competitive FPS muliplayer, there's plenty of alternatives), and Valve isn't taking advantage. To do so they would have to be preventing play unless people bought something, which they aren't. They simply provided an additional, fully opt-in set of features.
Finally, if you don't like playing with hats because it ruins some behavior you had come to rely on, find other people that feel the same way and start your own server and enforce a strict policy of exactly what's allowed. That's done often in serious competitive play anyways, isn't it?
Early on, the game had a consistent 1960s theme and each character had a consistent distinct sillhouette and behavior, so the game was easy to pick up and it was reasonable to play it competitively. It had great game design. Over time they ruined all of that for the sake of profiting off of addicted players.