Consider all the different schools of ethics which have sprung up

A few thousand years, and we've managed to come up with about three possible answers to the question 'what, in general, does one have most reason to do or want?'. Is your complaint that this is too many to have considered, or that the question isn't completely settled yet?

a standard if not unanimous approach is argue that the question cannot be answered by evidence

I know many philosophers who would be surprised by this assertion - I was under the impression the Empiricists pretty much won. In Ethics, particularly, moral observation is now a standard piece of the toolkit.

Of course, the grain of truth here is that due to the fractured nature of philosophical schools, there are large communities of philosophers who don't realize other large communities of philosophers even exist. In a sense, nobody knows what philosophy doesn't know, even philosophers.

My obligatory Edwin Jaynes quote on philosophers, quoting a colleague

"Philosophers are free to do whatever they please, because they don't have to do anything right."

Probability Theory http://books.google.com/books?id=tTN4HuUNXjgC&pg=PA144

"Philosophers are more susceptible to this failure mode because on many important philosophical questions, a standard if not unanimous approach is argue that the question cannot be answered by evidence."

No, philosophers are more susceptible because most of them can't recognize that "cannot be answered by evidence" means an answer can't be obtained at all.

To such individuals, reason is merely a passing fad coequal with every other way of asserting something, a fleeting hiccup that they're far too fashionable to consider important.

Is any of that avoidable?