All the people saying "DONT BUY IT BECUZ LOT BOXZ" don't realize that if the game didn't sell, companies aren't going to draw the conclusion that loot boxes were truly the cause. They aren't going to parse NeoGAF or a few Kotaku articles for a singular correlation of sales data. People don't buy games for a whole host of reasons, loot box fuckery possibly included. But there's no way for them to be like, yeah, the cause was definitely loot boxes if the game failed. All the crying about the end on a video game message board is the minority, whether you like it or not.
If you really want to show them how much you don't like loot boxes, buy the game if you enjoy it, and don't spend real cash. That's it. That's the secret. That's where they can draw correct data from and say, hmm, these dudes don't even like interacting with the money side of things. Doesn't help with the loot box problem as a whole, because unless you use a PC trainer it'll probably come into view at some point, but not spending cash is a good line to draw in the sand.