No you dont.
You need to truly believe in the cause, that you're willing to sacrifice certain things to advance the cause. Emily Davison believed in the Suffragettes cause so much she was willing to die to advance the cause, plenty of people believed in the anti-Franco cause that they were willing to potentially die when joining the International Brigades, Bobby Sands was willing to starve himself to death because he believed in the Republican cause.
None of those people above were thinking about whether they'd be able to get a job at the end of it, they believed in something bigger. As I say before dismissing them as "poshos"is pure laziness.