Disgusting as it may be, there are only a few options here, and none of them are going to make everyone happy.
If you leave them to rot in prison like you suggested, people are going to be upset that the society is paying to keep them alive(surely it would be better to get rid of them?)
If you eventually execute them like some countries do now, some people(like you) are upset that we make a show out of it - we don't. If one occurs it's a result of a judicial system that takes years to reach a final decision,and then we are "too humane" to just shoot people in the head without giving them the last meal.
And of course there is the last option of executing people on the spot - caught a child molester during the act? Why not shoot them right there, it is literally saving the taxpayer millions in costs of trials, judges,lawyers etc. No one can argue that it would not be a huge saving for the society. But I think we can do better than dispensing justice on a whim. As much as I enjoy Judge Dredd comics, I would not like to live in his universe.
Also, one could argue that a much better system would be about rehabilitation,not punishment, and in such system death sentence is simply not needed.