It is not easy to speak about evil things without veering into error oneself.
Islam, and if there were a more evil faith system somewhere in the world, whatever it is, would most definitely count as religions by any objective dictionary definition.
They would not, however, be what the founders of America intended when they spoke about religion, by which they meant belief systems that looked similar to Christianity even if they weren’t Christianity.
Islam is a religion like Jonestown Kool-Aid was a drink. No claims that either is salutary are made in the recognition.
But maybe I lied too.
Maybe the worst faith system isn’t even Islam. We know what it preaches even if we disagree with those things.
The worst faith system is probably the one that is almost but not quite Christianity. A form of godliness but lacking the power thereof (no effectual embrace of Jesus as a powerful Savior, though it may have a lot of rules that even quote Jesus quite extensively).
That one will fool a soul worst of all. It pops up in Revelation in the bible in the form of the ministry of Beasts and similar things.
I think Shariah is the system and Islam is simply a disguise. Islam is a worldly, materialistic religion in the same sense as progressivism. The prophet muhammed wrote the quran to justify his licentiousness, and his is the sole witness to the book.