If you want the game for multiplayer and the only way to play with everyone is to buy it, buy.
In all other cases pirate. It's not worth it to buy games anymore. A lot of games get updates which make them run worse. Some updates even remove support for some configurations so you can't launch the game. In other cases a game becomes unavailable for purchase because the publisher/developer craps out a "remaster" with a higher price-tag, higher system requirements, and a much larger install file.