My understanding is that when they got to the point of "becoming the Borg" from, whatever they were before, they essentially unanimously decided that this is better, more perfect, more efficient, clearly, this is the best path forward for everyone. Anyone who refuses simply does not understand how great and efficient it can be to be (what would become) Borg, so for their own good, we must assimilate them.

We see parallels with that in current society. One example I have sufficient knowledge of in order to cite, is the mistreatment of native Americans. The settlers started by trading with the tribes, which would have been fine if the trades were not, almost consistently done in bad faith. Later, the colonizers annexed their land, with a kind of perspective on it, like, you're not using this land (or not making very good use of it) and we know how to make the land more useful, so give it to us, or we'll take it.

Much later, native children were stolen from their homes and forced to attend schools "for their own good". Giving them information, but not necessarily something useful for their life in the tribe, just what will be useful for them living in a "better" society (the colonizers society). I've even seen entire reserves where their whole way of life has become a footnote, after colonizers swooped in, and built homes, which they couldn't maintain, with power, that they don't know how to manage, and plumbing, etc. Basically turning the entire reserve into a slum.

In essence, colonizers came in, said "we know what's best (for you)" and shoved it down their throats whether they wanted any help or not. We are the Borg, resistance is futile. Your biological and technological distinctiveness will be added to our own.... You will learn like we learn, and what we learn, you will live as we live, you will do as we do... or else.