Atheism (and anti theism): The *most* close minded faith (yes faith!!). Apart from the fake non-existent science/religion schism that they like to deepen, they represent to me the people who would have found it crazy and illogical for the earth to be spherical. Or the people who could NOT for the life of them give in to the fact that the Earth isn't the cent re of the universe.
Deism/agnosticism: A bit more complex since they do believe a powerful being (or that the truth is unattainable), but don't believe in organized religion. I think people who fall under these two groups are more often than not in a transitional phase of seeking truth and eventually tend to formulate or adopt ideas about the truth and nature of God.
Judaism: I think it's a religion based on God and God's word. It has strayed but not too much (and is the closest religion to Islam today). Unfortunately Judaism and Jews have been victimized, abused and their faith hijacked by political Zionist agendas. Thankfully some are smarter than the propaganda they're fed.
Baha'i: I don't know anything about their faith or why people don't consider them Muslim, but the two Baha'is I've met were very nice people.
I don't have time to think about them because I am finding out amazing things about Islam everyday myself, even though I have been a Muslim all my life.
Because however much knowledge I gain about Islam in my life it will still be like a drop in the ocean of knowledge that is available. Islam has answered all my questions, I don't need anything else