Wash is simply asking if his comrades are dead set on the idea of resolving their problems with gunplay, or whether they're open to a more benign idea, in this case going to see their friend Mr Universe to determine what damage has been caused by River's display in the bar.
In this instance, the line should probably read "wrong audience" (e.g. the incorrect group of people to be 'selling' something to), but these are a group of desperados we're dealing with, so they're also the wrong crowd (e.g. people who are a bad influence generally)
The line could be rewritten:
"Can I please make a suggestion that doesn't involve violence, or is this the wrong group of people to be trying to suggest that to, because you seem very keen on using violence to resolve this situation."]