Spoonbill hits the nail on the head, though I do think there are some rare occasions when it's prudent to decline to particpate in a procedural separation service.
It may, on balance, be safer to cross levels with another aircraft in order to get to higher altitude or perhaps VMC on top. Or perhaps 1000 ft of separation low down (say 2000 ft vs 3000 ft) may put you in busier airspace like an ATZ or the vicinity of a glider site.
[ 29 October 2001: Message edited by: bookworm ]