Again, I have no idea if Dahmer was forgiven or not. And it doesn't matter what kind of prayer he might or might not have said. Salvation is up to God. Period. I don't think I can't make that any clearer and the Bible is clear enough on that issue.
Let's see... Jesus said, "blasphemy against the Spirit shall not be forgiven", but you say that it can be. I think I'll stick with Jesus on this one. And, no, the other Gospels do not contradict this. Matthew, Mark and Luke are in absolute agreement here. John only refers to it indirectly in 1 John 5:16.
You also say that God can't stand insults but Jesus said, "Whoever speaks a word against the Son of Man, it shall be forgiven him". Since Jesus said numerous times that He is God, and was crucified precisely because He claimed to be God, again, I'll take Jesus' word over yours that God does tolerate - even forgives - insults, with the exception noted above about ascribing to Satan the works of the Holy Spirit.
As for providing the actual quote, I gave you the reference to do your own homework. Obviously it says nothing about sincerity and that was my point - sincerity of a prayer has nothing to do with gaining salvation. Asking for salvation doesn't bring salvation no matter how sincere the request. Salvation is a free gift that God grants according to His mercy, not according to anything we think, say, or do, however sincerely, because those things are "works".
Ron Paul - Honorary Founding Father