Not necessarily to extinction but to loss of control - I mean, becoming peaceful often means not investing in defence capability thus becoming weak, and becoming weak means inviting violence by opportunistic neighbours or inside groups.

It's a coordination problem - as any subgroup of homo sapiens that unilaterally abstains from violent power risks simply being overtaken by another subgroup that doesn't; you can abstain from using violence, but you can't unilaterally abstain from participating in violence started by someone else. "Si vis pacem, para bellum" will be true while humans are built the way we are.

A good example is Tibet.