It is not likely that those that have committed the most heinous crimes of mass murder will enter the Celestial kingdom. Its not that they won't be saved in the Celestial Kingdom, but that they are sufficiently selfish in thought and deed that they cannot (and would not want to) live in the presence of a Perfect God.
From D&C 132:26
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and if they commit no murder wherein they shed innocent blood, yet they shall come forth in the first resurrection, and enter into their exaltation. |
QUOTE |
and in none of these things did he(David) sin against me save in the case of Uriah and his wife; and, therefore he hath fallen from his exaltation, and received his portion; and he shall not inherit them out of the world, for I gave them unto another, saith the Lord |
The simple answer is knowledge. David knew what he was doing, and sinned against the greater light.
Now, I am not saying that Hitler or any of the others are likely to receive anything greater than a Telestial glory. But there is a real difference between David's acts and those of other people we are discussing. David was an anointed servant of God. Those we consider the most evil weren't or aren't.