The first reason, and the absolute disqualifier, is dynasty. In America, we do not have noble families with divine right to rule. Political positions are not inherited, nor passed from father to son or daughter like property. Two Bushes serving as president in living memory of one another is somewhat acceptable; three Bushes starts to look more like an undesirable pattern. I admit this is somewhat unfair to Jeb Bush as an individual; however, for the good of the nation, he should not run and must not win.
While Jeb gets points for transparency in releasing his official correspondence as governor of Florida, he loses even more points for failing to redact private information in the release, including social security numbers and personal email addresses of ordinary individuals. It is clear Jeb cannot be trusted to respect the privacy of citizens.
And if that wasn't enough, he's admitted that he doesn't understand the debate over the National Security Agency's collection of bulk telephone data. Anyone who doesn't understand why that program is a problem should not be anywhere near elected office, and has effectively admitted to being unfamiliar with the Constitution's limits on government, particularly the 4th Amendment. While not understanding the debate is bad enough, he has openly backed the surveillance programs.
In fact, he has praised Obama for keeping them in place!
This is absolutely a disqualifier. I will not, cannot, support a candidate who has said this. Not in the primary, not in the general. And he didn't just say it once, but keeps saying it.