That claim is incorrect. Independent surveys, including Pew Research, show that most Muslims globally reject violence by extremist groups. To assume ‘moderate Muslims’ secretly support terrorism is not supported by evidence.There is a big difference because mainstream Christian churches do not recognise, condone or support cults like the Klu Klux Klan while "moderate" Muslims for the most part, still support, fund and do not report Islamic extremist groups to the authorities. The goal of radical Muslims is to seek change in society in the long run, so their ultimate aim is to establish a social and political system that is based on sharia. This is why many so-called moderates actually support extremists.
If Christianity is not defined by the KKK, Crusades, colonial violence, or Christian militias, then Islam should not be defined by Boko Haram or ISIS either. Consistency matters.
Even your scripture warns against double standards:
Matthew 7:5 — ‘First take the plank out of your own eye, and then you will see clearly to remove the speck from your brother’s eye.’
Extremism is a problem of people, not the core teachings of any faith. Is that understood?