I’ll not pretend to understand mentality of people who describe legacy characters as somehow flawed or those who play them as inferior.  To me, all that means is admitting an inability to adapt one’s own world view as well as the arrogance to declare anybody who disagrees with you as simply “wrong”.  I could go so far as to describe the practice of discarding one’s characters after only one use as shallow and lazy, but that would only be me being spiteful.

Legacy characters gain the benefit of being established and better developed than ones made up on-the-spot.  More love and heart can go into a creation that persists than a simple one-off who will be forgotten in a year but I digress.

The simple fact is that both one-offs and legacy characters have merit.  Any GM can tell you all about that.  Arbitrarily condemning one or the other is a sign of weakness on the part of he accuser.  However, preferring one or the other is simple opinion.  I enjoy a mix of the two as a GM and, in fact, find the “disposable” one-shots essential for the random NPCs that don’t really matter.  A few, even, have gone on to become fleshed out and beloved additions to the party.