So if General motors was using slave labour to build their cars and feeding said labour with baby kittens, would you consider it a review bomb for someone to say 'You shouldn't buy the latest vehicle from General motors because of the way it is made'?

What if general motors came out and said that they think a great start to the day is to wake up and punch a dutchman in the face?

A review is, ultimately, a recommendation of whether or not you think other people should buy this product. If you can't recommend it because of something the company who made it did, to me, it's still a review. Because recommending that product is recommending financial support of that company. Not recommending it, is not supporting them.

For me a real review bomb would occur generally only in a case where a site like 4chan might suddenly spin a wheel of mayhem and pick a random game to just go shit on or something like that.