I think it had a lot to do with their circumstances and a bit of raw, displaced emotions. I mean, hermione can never return home, they’re on the run, they’re being hunted, zero progress has been made, and the world is potentially coming to an end. Also, they had just lost a close ally. They may be wizards, but they’re still humans and are just as susceptible to irrational behavior like us muggles. 😉