In the context of addressing the prior activities and positions of Supreme Court nominee Elena Kagan, Andrew McCarthy takes up the distinction between radical Islam and moderate Islam:

To hear progressives tell it, we can do nice, clean, friendly sharia, just like we do nice, clean, friendly Islam. “Lapidations,” [or stonings,] they will tell you, are no different from jihadist suicide bombings: outmoded vestiges of a long-forgotten time. Except they’re not. They are undeniably rooted in Islamic scripture, and they are happening today, with frequency, wherever sharia reigns. That is because the “moderate Islam” progressives like to banter about is a mirage in search of a cogent set of principles. There is no moderate Islam that can compete with the mainstream, sharia Islam. Thus the crimes and punishments, in all their ghoulishness, endure. …
Stonings are common in Saudi Arabia, where, as in Iran, sharia is the only law of the land. Beheadings are common, too. A vice patrol, the mutaween, monitors the population, especially the women, to ensure compliance with sharia standards of dress, prayer observance, and segregation of the sexes. Sanctions are draconian, as a 19-year-old woman learned in 2007, when she was sentenced to 200 lashes with a rattan cane after being gang-raped. Saudi Arabia’s crown jewels, Mecca and Medina, are closed to non-Muslims; forget about building a church or synagogue in those cities — non-Muslims are deemed unfit to set foot on the ground. The slave trade was still officially carried on in the kingdom until 1961 and has been indulged unofficially ever since. Slavery, after all, is expressly endorsed by the Koran (see, e.g., Sura 47:4, 23:5-6, and 4:24) and was practiced by Mohammed himself. The Koran and the prophet’s legends are the prime sources of sharia.

It would go too far to say that moderate Islam does not exist. Inasmuch as there are moderate people who adjust the religion to their underlying beliefs, it must. But moderate Islam will have difficulty winning the day for much the same reason that churches that adhere to Christianity Lite are fading: Over the centuries, religions come up with extensive answers to people’s common doubts and questions (a spiritual FAQ, if you will). But if those answers drift too far from scriptures and traditions, the religion loses its claim of authority. In countries that incorporate sharia into their laws (let alone outright theocracies), it isn’t a real option to simply stop believing (at least to the degree of letting disbelief change behavior).
McCarthy goes on to describe the creeping sharia of sharia-compliant finance (SCF). The likes of Kagan (for whom SCF was an issue during her time at Harvard) choose to disassociate this sort of sharia from the beheading-and-stoning-women-for-the-crime-of-being-raped sort But the link cannot be severed, because not only are the guiding principles of one the same as of the other, but Islamic clerics are necessarily intimately involved. And while they, individually, may be moderate, there is no mechanism for keeping out those who are not.