I'm not going to say that there isn't an overlap, because I suspect there is, but you'll have to explain (for example) which so many forms of identity politics, which by definition oriented around tribal loyalty, considered left-wing causes? For example, feminism, minority rights, and class consciousness? (Your average proponent of these causes are simply expressions of the more general fight against injustice, which is true to some degree, but your average skinhead will say the same thing about his cause.)
In general, I'd say that your average right-winger and your average left-winger (in American politics anyway) care the same amount about reducing injustice and harm but have radically different understandings of what constitutes injustice and harm and that's where the difference is.
EDIT: re "I'd expect them to be more inspired by an idealist past attributed to their tribe or authority." In my experience, as often as not, they are just curmudgeony.
You might be right. I'll confess to a limited knowledge of this subject :)
As for which groups have more tribal loyalty... maybe there is something to be gleaned from which have an easy time keeping their members marching in lockstep, vs which have a hard time with that.
In general, I'd say that your average right-winger and your average left-winger (in American politics anyway) care the same amount about reducing injustice and harm but have radically different understandings of what constitutes injustice and harm and that's where the difference is.
EDIT: re "I'd expect them to be more inspired by an idealist past attributed to their tribe or authority." In my experience, as often as not, they are just curmudgeony.