I'd like to give another perspective on this topic from the other side of the spectrum. Now, I'm definitely not the perfect example of every "purity lover" that has come to existence, so bear with me here. Obviously, not all people who desire purity in their characters are the same; there are of course the more extremists who overvalue such a thing way too much. But to us more, I guess, "moderate" purity lovers, I think it's just the thought of him/her being your "very first" just adds a sense of loyalty to the character, at least to me. It's just more appealing, I don't even know exactly why myself.
I'd also say that, while I "prefer" my fantasy women to be pure, it's not like I'll immediately hate them or something for their first being taken. It's more that I'll like them less than if they weren't. Still won't stop me from liking a character.
As to whether or not the game should add more characters like Saizou, Kagerou and Zero, I really don't care. If they add more of the less common trope of characters, that's fine by me, there are always other characters or other games that cater to the taste if we really care enough about it. I will admit though that it would make some characters much more interesting.