This article is from the Stand-up Comedy FAQ, by Steven Rosenthal and Steve Silberberg (email@example.com) with numerous contributions by others.
A. Some comics perform comedy to transmit their point of view to the
audience and hopefully make people laugh. If they bought/stole/used someone
else's material, they'd be no more than a talking monkey on stage
regurgitating other people's thoughts. Of course, some people have frail
egos and find the only thing that matters is for people to laugh at them,
regardless of whether the material was theirs in the first place.
So, sure I buy material.