Why do you lump Fundamentalists, Evangelicals, and Pentecostals with non-Christians, like Jehovah’s Witnesses and Mormons?

We don’t. We know the difference. You don’t find us saying, for example, that Mormons are Protestants (or, for that matter, Christians). But when the groups you mention use the same arguments against the Catholic Church or share common methods of proselytizing, it’s fair to discuss them together.