I'm not going to support the developers of a free game
Why do you feel the developers don't deserve your support?
Because they use microtransactions. I just want to play the game, but not support developers that use those.
If the game is not free to play, then you need to purchase it instead of pirating it. You don't need to use the microtransactions while playing the game, but you definitely should not illegally acquire it regardless of how you feel about their business practices.
I don't want to go against my beliefs and give a company money that uses microtransactions though.
If the game is free to play, then you can obviously play without having to give the developers any money. However, if there is an upfront cost, you need to pay that if you want to play it. If you don't want to support the developers, that's fine, but that doesn't mean you can pirate the game.