"China is a "repressive nation"? Says who? Britain, the leader in colonialist aggressions, mass slavery and blatant interventions to third nations?"

Yes, all true, in the past.

Decolonialisation, itself a problematic process, has occurred, and self-determination achieved to some extent for many groups.

When will the Peoples Republic grant self-determination to Tibet? That would be the action of a self-assured and mature state.