Because after the fact you're both clear and in your own minds. True strength isn't preventing anything bad from ever happening, it's to keep getting stronger and do better after the fact.

And letting something good like dating each other come from a shift is actually a good thing.

Keimi adopted me after the other one, but it was both our choices after the fact. Simply deciding nothing good can happen from the experiments because it taints them is too stupid. And it's weak.