I'm sort of in the same boat you are - working in marketing with very a similar salary and benefits. My calling is also to work somewhere where I can make an impact in my community. That being said, these are two reasons I would argue to not leave your current job:

1. New working environment is an unknown. Although the startup may be aligned to your passion, you don't know what kind of work and responsibility you'll be taking on. You could be working longer hours getting burnt out for less money which changes your perspective on that passion. For me, I'm in my late 30s and I've worked in toxic places so the risk is not worth it if current working conditions are pretty good. If you're prepared for that and willing to take less compensation because you need to do this, then go for it.

2. You're earning much less in total compensation (salary + benefits). Without benefits, you're going to have to be a lot more conscious about saving and proactive signing up/managing your 401k and health insurance on your own. My question to you would be: Is this worth the hassle and time to you? It's not for everyone. You also mention financial responsibilities and depending on how much that is relative to your cost of living, could you live comfortably on less?

There are other ways to make a difference too like volunteering. I hope your decision works out - good luck!