We shouldn't wait for them to come to our borders, so we get them in Iraq. As @
Abii said, unlike Iraq, they have no significant support base in Iran, in a country were the majority are either Shias or non-religious and the absolute majority of Sunnis do not approve of any extremist action and mentality. They won't be able to do anything to Iran except some random bombings in border areas and attacking border guards/posts. So it's important to kill as much of them as possible now.
And besides, you think if we don't fight them, they will love us? They are already thirsty for our blood. Last night, ISIL spokesman said they will also attack Iran, so it doesn't get any worse if we fight them in Iraq or in our own borders.
I wouldn't call it interventionism, I call it deterring a threat before it gets to you. Also, Iraq's government is very close to Iran, we should help them in these difficult times.
I don't think there will be any major direct interference by Iran like sending forces, but I believe Iran will ramp up training of different forces in Iraq to deter ISIL, it's the best way to fight them, asymmetric warfare. Regular armies are usually ineffective, even U.S army had difficulty dealing with them.