Start by asking yourself which non-fringe socialist/communist party was not using the Leninist model of organisation, and which was not a member of the ComIntern and its successors? Which did not receive funding and ideological schooling in the Soviet Union?
You have an uphill struggle against history against you.
> non-fringe socialist/communist party was not using the Leninist model of organisation, and which was not a member of the ComIntern and its successors?
UK Labour party? Has everyone forgotten the Fabians?
The modern Green parties tend to be "left" but not necessarily inheriting from the Marxist tradition at all, generally post-dating WW2 (although this produces endless arguments about "watermelons"). Also modern left-wing parties of almost all colours are explicitly pro-human rights, which includes not only the right to privacy but the right to property!
Again, I'm not saying that there aren't some actual pro-Stalin "tankies" around, but it gets incredibly tedious having to defend everyone to the left of the Daily Mail from automatic charges of being a Stalinist. Congratulations on your dozen posts of derailing.
Fringe is clearly a vague predicate.
One way of defining Fringe is via the number of followers that can be mobilised for political action. E.g. in the UK the Tories, and Labour are not fringe, but CISTA (Cannabis Is Safer Than Alcohol) is. In the Weimar Republic the KPD was not fringe, but the Socialist League was.
Start by asking yourself which non-fringe socialist/communist party was not using the Leninist model of organisation, and which was not a member of the ComIntern and its successors? Which did not receive funding and ideological schooling in the Soviet Union?
You have an uphill struggle against history against you.