Problem is, monarchism is not an American value. Having three members of the same immediate family hold the presidency makes America look like a third-world tin-pot banana republic where all the power resides with a handful of wealthy families.
If Jeb truly cared about (or understood) America, he would understand this principle, and would recuse himself from the race.
Many conservatives will instinctively reject this kind of dynastic rule. What was the point of rebelling against the English monarchy if the end result was to re-create it?
Holding my nose and voting for Jeb isn't the same as enthusiastically voting for him. Jeb isn't as bad as Romney but in no way do I want Jeb as the nominee. However, if Jeb gets it, I could see myself voting for him with no enthusiasm.
The dynasty argument makes little difference if Hillary is opposing Jeb. In all likelihood, such an election is either going to give to us Clinton term III or Bush term IV.