But is that really fair to William? To be in his late thirties and ruling?
It has been well-documented the negative consequences and effects of a young Queen Elizabeth II's rule -- how her frequent trips abroad put a strain on her young family's life as well as her marriage, how Charles, Anne, Andrew and Edward barely saw their parents. (This is also the case for other young monarchs, such as Queen Margrethe II of Denmark with her family. Crown Prince Frederik has said that he spent more time with his nannies than with his own parents.)
Just because some people dislike Charles because he is who he is, because of how he treated Diana, or because they dislike Camilla, doesn't mean that succession should be skipped in favour of William. In a way, that is a slap to both Charles and William: You are robbing Charles of a role that he has been preparing himself for his entire life -- and personal life aside, Charles has been doing a good job professionally in representing Great Britain. And you are also robbing William of a chance to live his own life, to prepare for his role as King as his father did with trips abroad and visitis within Great Britain, and to spend time with his young family.
Just because William is intelligent or has his mom's compassionate doesn't mean that he is ready to rule in his late-thirties. Not only would it be a great strain within the family for William to have succeeded his own father while Charles was still alive, but then the one thing about monarchy that is consistent -- it's bloodline and the passing of the throne from the monarch to his or her eldest child or eldest son -- goes out the window if you allow the picking and choosing of who should rule. Somebody could come along and make the argument that Edward is also intelligent and compassionate, so why not let the Wessexes rule and bypass the Wales' altogether? It's opening up a can of worms that throws caution to the wind with monarchy.