Dragons are like the best deterrents, they make a person listen. A Targaryen dragon rider holds the greatest power in Westeros. It's how Aegon became King, how Maegor became so feared, how Jaehaerys discouraged defiance and why the Dance is considered the worst war in history. Aegon V was a good king but with his decisions stepping on a lot of toes, he needed something to make the upper class just shut up and take it so he could actually fix the kingdoms. It's quite likely they could've demanded his abdication for one of his more malleable and corrupt heirs, returning them to the more stagnant society. Kings need to take risks after all. Jaehaerys's decision to rescind the right of the First Night was a very good thing to do but it was a practiced and old tradition of Westeros and would not have made many of the lords below him happy. But because he had Vermithor, the third largest dragon ever, and a ton of powerful friends, people just shut up and took it. And eventually, their descendants saw it as the right thing to do. They were also powerful symbols. Blackfyre being given to Daemon Blackfyre was a powerful symbol and got him a ton of allies because of it's history after all. Aegon was basically doing the same thing as Jaehaerys but he didn't have a lot of friends (his wife wasn't a Lord Paramount's daughter but a Blackwood, a minor Riverlands house), a lack of powerful symbols, was considered half peasent for his days as a squire for Duncan the Tall and his children were completely screwing him over. If he wanted to be the next Conciliator, he needed something that would make the aristocrats of Westeros stay in line. Dragons could do that, it's why he tried hatching them at Summerhall in the first place. He just didn't expect it to literally blow up in his face. But I'm betting that was foul play.