ISIS are arguably the most crazed death cult of our times. Consider how they burn their captured prisoners, throw homosexuals off buildings, and espouse a fundamentalist and primitive reading of Islam that has proven to attract disaffected Muslim youth in the West. A hands-off approach will risk a longer and more drawn out conflict, and will surely put the average American and average Syrian in more danger, even if ISIS are eventually defeated.
Helping Syrian forces wouldn't be interfering. If the Syrian forces are doing a good job, the U.S. should let them handle it, but I think that they should offer some help. The U.S. getting deeply involved in conflicts in other parts of the world has shown poor results in the past and often made the situations worse. The U.S. should just give aid and support to Syria, without taking over the entire operation and (possibly) making things worse.
No, let the Syrian forces deal with the fight with ISIS forces on their own terms, with help from neighboring allies in the middle east. The US in not in a position to have direct involvement in this conflict by means of a ground war, except as an aid to countnries requesting it. The US risks making the situation worse and creating nuclear war if the US does not exercise restraint. When the time is right and necessary, the US should interfere and help to dismember ISIS once and for all.
Syria as a country needs to fight the battles taking place within its borders. There's no need for the US to go and help unless the Syrians ask for it. Besides, there are plenty of nations in the Middle East who can give Syria the arms and the troops it needs to defeat ISIS.