It might have been correct for ancient Hebrews or ancient desert nomads to marry a sibling of a deceased spouse after their death. However, humans live to age 80 and beyond now and there is no need for such traditional and misplaced views anymore. Ariel Sharon shouldn't have married the younger sister of his deceased first wife--that's simply macabre and in poor taste. Neither of those people needed a reminder of the deceased in their everyday lives.
I feel like that is a betrayal to his first wife. I understand that she is dead but it feels like that would be wrong to do. I feel like the sister was in the wrong by marrying him as well. They should of thought about how the sister would feel if she were still there.
There is really no reason he should not be allowed to marry her. If the two want to be married then it does not really matter that he was originally married to her sister. Just being a relative does not exclude someone from being a potential significant other to someone.
No, it was not really wrong for him to marry the younger sister of his deceased first wife. She was probably a lot like his first wife by her personality and looks, so he most likely saw a lot of his old wife show through in her, making her perfect.
I do not believe Ariel Sharon was wrong in marrying the younger sister of his deceased first wife. This can actually be a common practice in some families and there is no reason to look down on it simply because it doesn't follow westerns society ideals. This is actually viewed as a good thing in some populations.