It's far far harder for a faction to defend itself when their enemies have massive air support and they do not.
Isis lose with or without boots on the ground if their current enemies in the region are simply given heavy air support and supplies.
Putting boots on the ground, Benefits:
More local control.
Better trained soldiers.
Cons:
Expense cash.
Expense lives.
Needing to run an occupation.
Difficulty of nation building due to resentment against your new state from local peoples about foreign occupiers.
Here's my op-ed that uses long-term orientation, probabilistic thinking, numeracy, consider the alternative, reaching our actual goals, avoiding intuitive emotional reactions and attention bias, and other rationality techniques to suggest more rational responses to the Paris attacks and the ISIS threat. It's published in the Sunday edition of The Plain Dealer, a major newspaper (16th in the US). This is part of my broader project, Intentional Insights, of conveying rational thinking, including about politics, to a broad audience to raise the sanity waterline.