In that case Osteen is not a liberal, he's just a prosperity, self-help preacher whom is a false teacher, not necessarily a heretic. There is a diff between a false teacher and a heretic. Osteen's teachings are unhealthy no question, but he is not in the same league as some others that I know of, or a Brian McLaren.
To me, you seem to be saying that people who call themselves Christian but believe liberal or humanist "theology" will be punished more severely in hell, because they are part of "the church".
But surely, if they are truly part of Christ's church, that is, if they really know that they need a Saviour, and have come to know that Saviour, the Lord Jesus Christ personally, they won't be going to hell at all.
Perhaps you meant that
the liberal/humanist organisation they belong to calls itself a church.
But then, that doesn't fit your argument, because the Mormons also call themselves a church.
("Church of Jesus Christ of Latter Day Saints").
I'm assuming in all this that you are using the word "liberal" theologically, not politically.
You really need to read some of Dr. MacArthurs books, specially ones like the Truth War. If you did read it, then read it again and look closer. He does make a strong case against heretics inside the church being more deadly than Mormons, etc..
But isn't this something different to what you posted in the OP?
There, you wrote: "There is no question that the Christian Liberal/Humanist will have a hotter hell than the Mormon because they are in the church and pretending to be the real deal."
I took that as meaning that you believe punishment will be greater for one group than the other.
Now though, you seem to be talking about the effects on a church brought about heretics calling themselves Christians coming into a church and spreading their heresies, and comparing that to Mormons doing the same thing.
I agree that someone pretending to be a Christian is (humanly speaking) a greater threat to a church, because the danger is hidden.
"Wolves in sheep's clothing" comes to mind.
A Mormon coming into a Christian church is a more obvious danger, unless he/she is, like the heretic,
pretending to be a Christian.
Degrees of hell could be argued one way or the other.
Seperation from God is seperation from God, regardless of who.
There is one reason for seperation from God, and that is a rejection of Jesus Christ as Savior.
Degrees of hell is like getting an F+ instead of an F on a report card.
There are many threats to the local New Testement church today.
Mormonism is right at the top of the list.
People like this are the ones who come in and rip a church apart, if'n you ask me. satan has more "members" in church than God does, if you ain't too careful.