There's limited and local skepticism, based on serious reasons for doubt. That can be a very good thing. (One ought to be skeptical of what politicians or advertisers say, for example; we've got plenty of evidence that they're often less than reliable sources of information.) But then there's more global skepticism that calls into doubt in a wholesale way large swaths of what we normally believe -- typically not on the basis of specific reasons for doubt, but rather on the basis of top-down arguments.

Many of us (not all) find the second sort of skepticism less than helpful intellectually. One reason: starting out with that sort of skepticism cuts of interesting lines of philoosphical inquiry before they get anywhere at all. Unless we set that sort of skepticism to one side, most philosophical projects don't even get off the ground. For example: if we start from the point of view of ethical skpeticism, then serious moral inquiry gets stopped before it even starts.

There's another reason: at least some philosophical skepticism seems just too philosophical to some of us: seems to give too much credence to high-level arguments of a certain sort, and not enough to intuitions that are closer to the ground. But this is disputed territory.