Just to build a little on what people have stated...
I have a "theory" as to why MKIV owners and the other Gen Supra owners don't seem to get along...
And that is that most MKIV owners are NOT Supra guys (Let alone Toyota guys), they're just MKIV guys... Guys that are in NOT just to appreciate what a great car it is, but to down right show off to others their x,xxxWHP numbers...
Most that own a MKIV have "other" brand name cars in the same stable, while most MK3 owners being the good Toyota guys they are as well will own other Toyota vehicles... To most MKIV guys, the link ends with the MKIV... We can thank F&F for that!
Most MK3 guys on the other hand ARE NOT ONLY Supra guys, but also TOYOTA guys as well... and at the same time, they are CHEAP! That embarrasses the usual MKIV owner who is only in for the status... They don't know much about the MK3, and when they do see one, is all broken down and with mismatched parts and homedepot parts!
I think that's where the issues begin... most MKIV owners want to stay away from the (according to them) retarded older brother while the retarded older brother wants to stay close, but eventually gets tired of getting blown away and eventually feels resentment and don't want anything to do with the younger brother ...
Other things affect difference in owner crowd as well, but those are more related to the purpose the cars were built for. For instance... there were 956 meetings to discuss weight reduction ALONE for the MKIV... That completely changes the purpose it was built for from the MK3, which was the opposite...