Both ISIS and the American Left are both extremists and are nutjobs. Both have nutjobs in their political parties. Not only are they nutjobs, both ISIS and the American Left are very armed and dangerous. ISIS and the American Left are often very destructive in their protests by destroying property and hurting innocent people often to the point where their own actions are willfully considered as acts of terrorism. ISIS and the American Left often get very destructive during their protest.
Both of these groups excuse the preaching of hatred towards disfavored ethnic groups. Such as hate towards Christianity and Judaism when our constitutional democracies that all stem from Judeo-Christian roots. Both excuse violent attacks by Muslim terrorists citing "Islamophobia" or using Islam as an excuse.
Neither of them believe in free speech of even the tiniest criticism. The partisan line between both parties is blurred. There has been more butchery from leftwing ideologies than from the right wing ideologies. ISIS hates free speech and freedom of speech more than the American Left does. The American Left values free speech and freedom of speech more than ISIS does. The American Left is not as violent towards free speech as ISIS is. Although the news media portray the American Left as being violent against any forms of free speech.