Satan must laugh when he succeeds in sowing false doctrines in the church. He must laugh harder when atheists attack those doctrines (because they know they are either ridiculous, evil, or both). And he must laugh harder still when well meaning Christians defend them.
One such doctrine is the doctrine of eternal torment.
"...I think no other doctrine can even compete with "no further chances" in terms of the following three factors. No doctrine even comes close to a) being so strongly believed by so many evangelicals despite b) being so utterly disastrous in its consequences and c) having so little by way of Scriptural support." - Keith DeRose
An example of the kind of harm it has done is explained here. Because such a "great many teachers" support the doctrine, it is time it is addressed. See here.
A doctrine which is almost as harmful, and just as false, is the idea that God poured out his wrath on the innocent. See here.
There is no evidence to suggest that the thief on the cross accepted any theory of atonement (see here). But he did all he could do. He admitted he was a sinner and acknowledged Jesus. I'm sure that if he had of come to Jesus in different circumstances he would have had a living faith; he would have loved and obeyed him. You don't have to accept a particular theory of atonement to accept Jesus (see here).