Eliezer has said something wise on exactly this point...somewhere. It is somewhat in contention with what you say here, or at least how you say it.
If your foundational principle that you program into in AI is that slavery is bad, taxes become impossible to collect.
Was Eliezer really embracing taxes as good, here, as you imply? Seems like more of a consistency argument against taxes.
From a consequentialist point of view, it's not obviously invalid to say no taxes should ever be collected. Humans naturally think in terms of rules, your term "consistency" was a fine one. Hence, in the real world, the consequences of things include how they interact with this delusional proclivity of ours.
For this reason, the slippery slope argument is often not a fallacy. As used it often is a fallacy when an arguer is sufficiently mistaken about the degree to which we think in terms of rules. "If you allow barbers to cut hair, before you...
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: