Megumi knows that the one and only who ate a cursed body part on the spur of the moment wouldn't certainly be able to slither his way into his life. Itadori Yuuji is reckless, he thinks more with his actions than with his brain; his instincts might be good and well based, but his urges can be dangerous at best. Megumi doesn't fully understand how someone like him can hold that much power and control to sustain Sukuna, but that's one of the many things he can't comprehend from the other. Itadori is the type of person in their field of work that needs constant surveillance, someone to make sure he doesn't snap or walk directly into a trap. He believes that Itadori needs someone to be there and look out for him, making sure he doesn't die, and he will not be the sort of person to succumb to it.