Your analogy is analogous to swiss cheese. It's near given that a volunteer firefighter will encounter a fire. However, most startups fail and provide poor job security. Equity should not be factored unless it is a tremendous amount. A couple percent is a joke. 10% and up becomes reasonable, and should be understood to be merely a bonus for working for an early-stage company.

Just the job security alone is enough to balance out the equity. A shitty salary is not an excuse.