As a fellow Muslim, i am not agreeing with ISIS or support it and not to blame them as well. As long as the Mahdi haven't been showed in Mecca .And also, if ISIS is the real khilafah, God had been bless them and gave them Mecca and Madinah easily. So what the prophet Muhammad hadith means about the black banner army that black banner will come along with Mahdi, is not the current black banner (ISIS, Hizbutahrir etc). Even in the future if the black banner could be from the ISIS it self, the Mahdi have not showed and the obligation to follow the black banner is need to be hold.
So my stand is not to supporting them and at the same time not to blame them , because most of mainstream media like in US, Europe and even Al Jazira are tend to be lie as well. I will wait and see, waiting for the order from the local trusted Imam is the right choice . As for the whole war affair i am fully supported FSA that fight with the Shia. Also the involvement of US and Rusia actually make even worse, because US here actually trying to eradicte everyone , especially all the seed that will come to help the Mahdi, while Rusia is trying to defend Iran and Shia.
If there is a muslim who still want to support ISIS, my advice is, please not to be hasty, because we dont know the real situation on the war. When the times come Allah SWT will show us when to fight, just be patient and just help the Syrian, Palestinian, and Ethopian civiliant by donating, ofcourse with the trusted local organization on your own country. Dont worry khilafah will stand again with Imam Mahdi and all the Muslim will be united under one leader, and there is nothing that can stop them. But for now we better prepare with studying more about Islam, and trying to be active on local Masjid.