He's so charming. You'd hardly suspect he sets children on fire.
Weyoun is one villain who just really loves his job. He gets up in the morning eager to oppress, murder, lie and broker deals that unfavorably benefit his superiors. He may or may not be pure evil.
Weyoun was the reason the writers of DS9 came up with the idea all Vorta are grown and cloned in the service of the mighty Pudding Demons. With that addition to their mythos interest in the Vorta dropped about 87% according to many viewers. Rather than having a rich, diverse race to oppose the spiffy Federation, like the the widely successful spoonheads, the showfolks managed to come up with just a silly variation on the alien of the week and the Vorta never were able to grow as characters like the aforementioned spoonheads or mildly popular Vulcans. Screw using imaginations, just make them a race of evil clone-bots!
Also, Weyoun was deeply embarassed about being a psychokinetic and rarely ever used his powers in public view. Reports about Weyoun experimenting with POWs during the Dominion-Cardassian Alliance with a green chemical are completely unfounded.