One of the most important features of good politics is that it recognises that private power is at least as dangerous as public power, and that people readily use any power they have to control others unless it's trained out of them with good laws and traditions. From the business owner as a low-grade dictator to family demanding their children do not date or a community forcing "modest" dress on its members, we should be wary of and attempt to mitigate/prevent the harms from private abuse, possibly with public power. The theoretical "ultimate escape" people have in these situations; to leave the family, to divorce a spouse, to walk out of a community; these are insufficient for justice in the same way that a nation that invites dissenters to emigrate is. It's nice to have that ultimate escape valve, but it is often insufficient.
There is a difficulty intrinsic in this judgement though; a strong public sphere with weak subcultures and permeable borders prevents these abuses, but creating/maintaining that state-of-affairs is a best-effort task; some parts are easy (mandatory public schooling, preventing mediation from effectively taking law out of the public sphere, etc), some parts are harder (in conception, political wrangling, and implementation).