Oh yeah defeatism is a super common response. There is no way to logic them out of the defeatism, this is why revolutionary movements didn't just have theoretical and logical messaging in their propaganda but also other things to keep people from falling into defeatism. It can help to really hammer that message of "a better world is possible" into their heads, or offer the prospect of building worker power as a responsibility that workers in our moment in history have to the generations of the future, so they may live in a better world. Then you just need to convince them that every little bit counts, and unions are the most important part of our current moment in history for establishing political power as workers.