While they definitely deserve punishment for being overzealous with their jobs, there is appearances to keep in mind. Killing servants of the person employing you isn't a good look. Especially since adventuring is heavily reliant on trust and reputation. Waiting to deliver judgment until Touma's fate is ascertained is a reasonable decision.
Also, I can relate to Maria in that last page, even if it felt a little rushed/slapdash. Sometimes you can understand why someone did something, but that doesn't excuse what they did. There's a key difference between the two that people really seem to forget more and more nowadays. There's value in being able to empathize with and understand someone's logic, even if you don't agree with it.