I’ll contend till the day I die that the slippery slope fallacy isn’t a fallacy. Taking things to their logical extremes and then walking them back reveals a lot and is often prophetic. It’s not a way to “win” an argument but it certainly helps clarify thoughts and suss out details. Your taxation example is perfect. “What does the world look like if tax rates were 100%?” “Ahh ok, then why is 25% better than 15%” or better yet, “if a tax rate of 100% is slavery, what do we call a tax rate of 50%?” Contending with the results of the slippery slope “fallacy” is required when making a political point as it pertains to policy because history has borne out time and again that movements will be taken to their eventual extremes.