In terms of their ideals there is not much to separate them anyway
As ISIS is being increasingly squeezed in Syria and Iraq growing numbers of its fighters want to get out.
Their best bet is reaching Syrian rebel-held territory and from there on to Turkey.
Financial Times reports the rebels have recognized this as a good business opportunity. They are now charging fees to fleeing ISIS fighters, or which is even more lucrative, sell them to their home countries when these want them back:
Most rebels say smugglers charge between a few thousand dollars and $10,000 just to cross from an Isis area to rebel territory. It can cost another $10,000 or more to enter Turkey, they say.
“It used to be only the smugglers doing it, but the rebels saw what was going on and thought, why shouldn’t we benefit? We’re the ones who control this territory. So, it’s become a competition,” says Abu Yazan.
“The countries inform Turkey, which will pick up the person from the faction,” says another rebel figure who has been involved in such trades. “There are countries who pay money for it. What you can make [on a foreign fighter] always depends, but usually at least $50,000.”
But the rebels are not reaping monetary rewards alone. The majority of fleeing ISIS fighters wants to reach Turkey so they can reenter Syria in Idblid and continue the fight in rebel ranks:
Rebels say more than half the Isis defectors seek to go to Syria’s Idlib province to join other jihadi groups that have links to al-Qaeda, suggesting they have not given up on their extremist ideology.
The split and conflict between ISIS and the rest of the Islamist rebellion since 2014 has been real but it was always more about strategy and leadership rather than ideology. An individual jihadi fighter can easily feel at home with either.