I agree to some extent. However, I don't agree that they start "too pure". They start too stupid and pure. Irrelevant how pure you are and how you despise anything sexual, it's simply stupid to let someone for example make nude photo of you because he tries to blackmail with upskirt photo. I have a problem with motivations, not actions. If blackmailer had for example completely non-sexual leverage (fear, money etc.), it could be fine. If she was already not-so-pure she could use his "blackmail" as an excuse "it's not me, it's him; I don't want it but I have to", so that she can strip withouth feeling guilty and it could be ok.
So, my conclusion and advice for any dev is: think well about motivations in a corruption game. Using blackmail is ok, but it has to have some logic. Make your MC pure, but do not make her an idiot. She can be naive (for example be trusting to a fault), but not stupid.