Would you prefer a lowly street rat run things, one who as a scoundrel is mostly lucky and a bit acrobatic as his only real positive traits?
Technically Jafar had no interest in the princess until Iago planted that suggestion when, at that point, he was already unraveling from the stress. Imagine how Jafar might have seemed in his life before the movie, by the time we're shown who he is he's already been through enough to justify these sorts of actions to himself.
I'd technically throw the blame for how their society is going on their traditions, the very ones that'd allow The Sultan to be in power in the first place. Can we really blame Jafar for a corrupt system based on royalty that precedes him, that is much bigger than him, to the point of shackling him to The Sultan in the first place?
Edit: Consider this scene (that I couldn't find on Youtube):
With both the Sultan and princess out of sight, Jafar grinned angrily. He was thinking about his failure of getting the lamp from the cave of wonders. "If only I had gotten that lamp," he said.
"I will have power to get rid of you," Iago imitated Jasmine before complaining, "DARGH! To think…we gotta keep kissin' up to that chump and his chump daughter for the rest of our lives."
"No Iago," replied Jafar, "Only until she finds that chump husband then she'll have us banished, or beheaded!"
Both Jafar and Iago had the scary and disgusting thought of losing their heads if they were beheaded. Suddenly an idea popped in Iago's mind. "Wait a minute, wait a minute Jafar. What if YOU were the chump husband," he said.
"WHAT," replied Jafar in insult.
"Okay, you marry the princess alright," said Iago, "and, and uh…you…and…you become the Sultan."
A happy grin grew on Jafar's face. Iago's idea seemed like a good one. "Marry the shrew? Become the Sultan? The idea is merit," said Jafar.
"Yes, merit, yes. And then, we drop papa in law and the little woman off a cliff," said Iago, who then dive bombed himself to the ground, "KERSPLAT!"
Jafar laughed at how diabolical that idea was. "I love the way your foul little mind works," he said as he and Iago started laughing evilly.
I'm telling you, Jafar's a victim of circumstances. If anything Iago's the bad guy and, hilariously, frames it towards Aladdin that he's the victim as a way to worm his influence towards the newest source of power in the sequel, and the 'good guys' just accept his version of the story as the narrative otherwise does the same.
Consider that when he's losing his shit [1][2], he's both discovered that Aladdin was using the lamp to pretend to be a prince and now has The Sultan ordering his palace guards to behead him on sight, having just escaped with a smoke bomb. This isn't Jafar on his best day, but rather as he's unraveling as pressures mount and years of planning fall apart.
A lot of Disney movies offer a lot of room to sympathize with the bad guys once you consider their subtext rather than merely their appearances.
Ę̵̚x̸͎̾i̴͚̽s̵̻͐t̷͐ͅe̷̯͠n̴̤̚t̵̻̅i̵͉̿a̴̮͊l̵͍̂ ̴̹̕D̵̤̀e̸͓͂t̵̢͂e̴͕̓c̸̗̄t̴̗̿ï̶̪v̷̲̍é̵͔