Should a programmer you hire be able to reason about CS problems? Yes. Do they need to be able to write out the best possible solution to a problem on a whiteboard within 15 minutes? No.

The white-board sessions only really serve to intimidate people who aren't good public speakers, think better with some time and peace and quiet, or simply haven't bothered to memorize code they never have to write from scratch.

Legitimately bad candidates could just as efficiently be eliminated by having a casual discussion about a CS concept that relates to the job description.