What’s the difference between the following christian sects? I hear catholics don’t like non-catholic christians, and regular non-catholic christian’s don’t even consider catholics to be christians themselves despite them both worshipping Jesus… what is this about?
The separation is due to differing beliefs. Separations between xtian churches happened when someone who disagreed with the leadership had a big enough mouth to create their own following.
The big distinction xtians tend to make is between "actual christians" and heretics. Generally, if you disagree with the text of the Nicene creed, you are considered heretical. This would include churches like JWs.
The rest that follow the creed are generally either protestant churches or churches that had non-fundamental disagreements in the church's infancy. These are considered officially xtian, and only really get chastized by catholics and orthodox christians, as these churches view the protestants as "sectants". "Stupid, but their heart is in the right place" kind of attitude.
As far as the purpose of this, xtianity does not need to be monolithic for it to still further the goals of messianic prophecy. So when people pushed against a monolithic church, they were able to freely (mostly, there has been infighting) found their own church.
If you're a popular xtian preacher and want to found your own xtian church, depending on your beliefs or who is the ruling church in your area, you might get called a sectant or be considered a heretic and chastized by popular christian religions. These "heretic sects" still can be popular, though. And as long as you worship jesus as your god, (((god))) is happy with that.
