As the king does, so does the people.
What if the son doesn't make a great king? What if he's nothing more then a glorified tyrant? What then? Histories of kingships is filled with them. One king was truly a great and noble monarch, yet his son's were moronic patsy's that ruined the kingdom. however the king acts, so do most of the subjects. If you have a good king then the kingdom is good. If you have poor (or evil, if you will) king then the kingdom is poor.
The founding fathers recognized the dangers of the monarchy. It is why we have our system of government today. Instead, they wanted a form of government where the government was answerable to the people (outside of utter rebellion) and where the people themselves could serve the government. You can't get that in a monarchy. In a true monarchy, the people are there to serve the government and king. If the king respects the people, all is well. If the king does not...In a democratic republic like our own, we have the power to remove the 'bad' kings and keep the 'good' kings every election cycle. you or correct, some senators sons have been great senators themselves. If they are good, I'll vote them back into office (and some of our senators have had longer reigns then most kings did) if they are not I'm glad I have the freedom to vote them out of office.
No, I am very glad that the founding fathers had the the wisdom and understanding to avoid the pitfalls of a monarchy. Instead of our freedoms being dependant on the mood of a man, our freedoms are guarenteed...even to the point the government cannot take them from us (itleast in theory).