Yup yup.. I thought so too.. But then, from Sakura's point of view, Mizuki can satiate his bloodlust from anyone so he isn't someone special.. That's why he wanted to protect himself from getting hurt.. Just happy Mizuki returns his feelings! (⌒▽⌒)
He had the option to drink blood. Semen isn't the only thing he can consume in order to survive. What he did was wrong and that's that.
Well, if it was established that he could easily find blood as an option in that time, then, circumstance decreases the "validity"of the act. Or at least increases the "wrongness" of the act, I guess.
Ofc by easily, I mean without having to take away blood from others unwillingly or resorting to stealing blood bags from hospitals. So yeah, if he had easy access, that would have increased the wrongness of his act.
Although,I did find it a bit unfair. Mizuki needs to feed off of someone to survive, I think it'a reductive to see it as cheating when he could have died or sth if he did otherwise. I just thought Sakura needed to understand that.