Y'know I love Comedically Ineffectual Javert but I feel like. Mayhaps. Not enough emphasis is put on how he is actually dangerous to people on the barricade.
He's a government spy -- "A spy of the first quality, who had observed everything, listened to everything, and taken in everything, even when he thought that he was to die; who had played the spy even in his agony, and who, with his elbows leaning on the first step of the sepulchre, had taken notes."
He knows everyone who was there, and a good amount of who did what, who's the leader, etc. He recognizes Marius after the sewers . He took names. He could have given evidence against everyone on the barricades.
Including the five men who escaped.
Including anyone who survived the massacre.
Including the women who worked at the Corinth, who did in fact help set up and prepare the barricade for the fight.
In fact, we don't know that he didn't --we can assume that he had too short an audience with the prefect to give over any detailed info, or that he chose to withhold some things in his Valjean-induced confusion, or even that they threw out his info after his suicide. But it's also possible that five men who thought they'd escaped were rounded up and arrested that week, or that two waitresses were seized as insurgents, or captives were hit with some very specific charges. As Hugo examines in detail in Ninety Three, and hints at even in Les Mis, sometimes showing mercy to one person means condemning many others.
(This , combined with the then-current attitude towards spies --basically that they were the scummiest of scum, execute immediately-- all makes me wonder not why Enjolras wanted him killed, but why he insisted on letting Javert live so long. Especially after Prouvaire's death, when it's safe to say the idea of any potential hostage negotiation is nixed-- what is the point? They aren't really intent on saving a bullet, given Valjean has the go-ahead to shoot him. And after Five Less One More, there's no chance that, say, they'll win and get to let him go as being actually harmless to them with the new political situation. There's no real explanation given in canon so it's an interesting question!)
At any rate: whether Javert did or didn't actually deliver his info, Enjolras and the other barricade fighters choosing to execute him is a practical move totally in keeping realistic military behavior (and Hugo is trying to establish them as behaving like Honorable Military Men ! Which is a whole other topic ...) . Javert is dangerous to the barricade fighters , as his job is to be dangerous-- and despite how he comes off sometimes (and in some adaptations), Javert is actually very very good at his job.