I always find Mumsnet really interesting on this topic.
Some MNers seem to take ABE attitudes deadly seriously and very personally. While of course not all Scots think the same way on this topic it’s not really as “bitter” or agressive as many posters seem to assume.
Scotland has its own distinct cultural identity, we arent just North British. Quite a lot of ABE is just asserting that cultural identity.
Part of it is rivalry based, if you have a local rivalry between two sporting teams you naturally cheer for whoever their opponents are, ABE is just that on a bigger stage.
Remember too that the relationship between England and Scotland is asymmetric.
Saying “but I supported Scotland” isn’t in any way the same,
Scotland doesn't have a centuries long history of political and military oppression against England. (And if the Falkland’s War upsets you think about how you’d feel if Argentina had four hundred years worth of aggression towards England and was still running roughshod over your political decisions)
In my experience very, very few people are actively anti English. Most people have English family members, friends, neighbours, colleagues etc etc
Saying ABE is not saying “we hate the English” it’s about asserting our identity as separate to a larger, stronger, frequently thoughtless and not always very kind next door neighbour.
ABE is generally said with wry good humour. I get that Scottish sense of humour is different to English.
Think of it this way, if a little kid has been bullied for years by a bigger kid, it’s fair enough to have a bit of a giggle if the big kid drops his ice cream. It not really much deeper than that.