ISIS is a perversion of the Muslim religion, and Muslims want to fight ISIS as much as any other group of people do. Questioning this is like questioning if Christians want to fight the KKK. The KKK does not represent the majority of Christians, just like ISIS does not represent the majority of Muslims.
Muslims are just as angry about ISIS as the general population is, if not more so. There are many Muslims who are working to fight ISIS in a wide variety of ways. Some have even joined the military or the CIA in an effort to stop ISIS and other terrorists.
Yes, some Muslims are serious about fighting ISIS. It may be difficult to recognize this fact clearly because not all Muslims are the same. Asking whether Muslims are serious about fighting ISIS is like asking are Christians serious about fighting ISIS. Yes, some Muslims are serious about it. So are some Christians.
Yes, Muslims who are not a part of ISIS are just as serious about fighting ISIS as other people. People want to feel safe and secure. Muslims feel that ISIS is a threat to this even if they are Muslim. Thus, it does not make sense to believe that Muslims that the majority of Muslims support ISIS.