Maybe I was ambiguous. I was referring to 'error skepticism', and 'regress skepticism' rather error and skepticism as distinct entities. But your latter explanation answers my query; I am, however, unimpressed with that response.
To summarise: (1) skepticism is self defeatist, and (2) skepticism offers no ethical foundation. I'll refute each in turn.
(1):
Skepticism is not a proposal, i.e., "Knowledge doesn't exist." for that would be contradictory. Skepticism can be seen, within the Western tradition, as the philosopher's conscience. It asks: "If we prescribe to 'X' can we prescribe to 'Y'". Skeptics posit hypotheticals, not absolutes.
Consider the hard skeptic, he holds nothing - not even that nothing can be known. It's a dark room, but that metaphor can only get us so far because the skeptic can't even know that the room's dark. Skeptic's arguments go thusly, "I cannot run arguments in my metaphysic; however, I see you have a different metaphysical system and I see that within yours argument 'X' would be possible meaning the system collapses in on itself".
In that way skepticism is not contradictory, if you'd like to hear the skeptic's arguments (that run in your metaphysic) ask me to elaborate.
(2):
There's no logical bridge between what-is and what-ought; your metaphysic does not change your ethic; for example,
(1) Humans are egoists. (C) We ought to make egoist choices.
That doesn't follow; we'd need another proposition, namely: (2) The right thing to do is be true to ourselves. So now we have two distinct propositions (1), which is metaphysical, and (2), which is ethical. We see that any ethical conclusion must admit an ethical proposition. But now we have to support prop. (2), which can only be done using another ethical prop., a la, infinity.
Conclusion: there is no bridge between is and ought. (G.E.Moore)
All that is to say, nobody can act on the basis of a metaphysic.