I don't think they all say that, otherwise what would be the point of hell?
Hell and Heaven are defining points. It's impossible to have a scale with one point only.
Also, there is such thing as apocatastasis. It's another proof that we will all be in Heaven, even Satan.
I'm pretty sure I've read rants by the Westboro Baptist Church promising Hell for gays and unbelievers. Are you saying they're wrong? And if they are wrong, how do you decide which Christian sect is correct?