Y'all are missing the point. The MC wasn't equating their actions at all, and he fully believed the rapist was the worse person by virtue of being a rapist. He realises that, regardless of the other dude being worse, he's still being irresponsible by shouldering her burdens. He's a good person for doing so, but it's irresponsible and it can't last forever. He doesn't have a plan, and there are certainly going to be situations where it's going to be bad for him (such as if she's unemployed). She's not his daughter, and he can't treat her like she is because that will only cause problems for both of them.
tl;dr he's not thinking he's as bad as a rapist, he just realises he's being irresponsible by helping Sayu.