The slippery slope fallacy here does not apply.

It is absolutely a fallacy to say we can't possibly levy a tax on a billionaire lest it, ultimately becomes a tax on us.

Already they have a pretty sweet deal compared to most folks, most folks have most of their 'wealth' taxed as property. Since real property is a tiny sliver of their 'wealth', they get to keep more percentage wise than the random person, despite needing it less.

To say any tax might evolve into a tax on the common man is like saying we can't regulate nuclear weapons, lest it becomes a regulation preventing people from having scissors. Yes, there is the example of income tax and a mistake was made at the time they went to expand it. The problem was not the initial tax, it was the point of expansion. There's no reason the expansion of the tax should have any lower barrier than getting it levied in the first place.

Now if you argue that the measure was somehow flawed in that it failed to limit the scope and explicitly opened the door to things, but it was the opposite, a one-time, billionaire only scoped event.