I think they're saying if you start out that way naturally (like a peaceful sapient race on a peaceful planet) they'd be an easy resource for something less peaceful (it would just take one aggressive race to extinguish them). If peacefulness and powerfulness scale together during a species's development, they may learn to learn strategies for peaceful coexistence before the stakes are too high for screwups.

No. The very tribalism that has allowed us to survive now works against us because we were too successful at survival. The solution is to be aware of and constantly fight against our base selfish instincts through things like what you said. The problem is that we seem to always go back to "fuck you, got mine" as a species. Perhaps the great filter is that a species that's successful enough at survival to get to the point where space travel is possible will always be betrayed by the tribalistic behavior they needed to survive the harshness of life.