In order for an ideology to exist, one must find people who embrace that label. You won't find on earth any self-described Islamofascist. There is no "Islamofascist Manifesto" out there.
The only people who use incorrect terms like Islamofascism are neoconservatives who are too afraid to label Islam itself as the problem. Islam is bad enough. There is no need to make up a label for something that doesn't exist. Labels matter.
Coining a word, or expanding the meaning of a word, is fair game in the English language.
Fascists did not - as communists did - subscribe to materialist philosophy. They did not believe that matter is the primary reality and that economics is the kernel of society or the engine of progress.
Fascists did want to liberate Man from the past, yes. In a sense, they wanted to liberate the West from what they considered the degenerate values of Judeo-Christian history. But they also wanted to return to the past; they wanted to return to Rome, to the pagan world, to the world of war and conquest.
The similarity between Islam and fascism is more than skin deep. Both movements deny the Enlightenment, reason, equality, the immorality of slavery and domination. The only real difference is that fascists believed that their holy law was written in Darwinian Nature; the Islamofascists believe it is written in the Koran.