Encapsulated in that “etc.” in my first response is “going out of business”. This type of response would be way too difficult to get actual numbers for, but it has worked countless times. Just look at all the businesses that are no longer in business at all, they went out of business because they were no longer earning enough to stay viable.
It doesn’t matter if the company connects the loss to a specific action (although it would be nice) since the end result is the same, after enough time.
Lastly, I just don’t like the idea of my dollars being used by a company to further an agenda that I don’t want to support.
Not commenting on the argument, but just FYI: “Slippery Slope” actually refers to an argument that could include a slippery slope fallacy, but not necessarily. A slippery slope fallacy is an informal fallacy, meaning that any errors are in the content and not the format of the argument (i.e. the slippery slope argument itself).
Just an aside, but it may help others who have this issue to share the solution that worked for you