There is no room for an ethical sexual relationship […]
They didn’t argue otherwise - you’re attempting to attack their position on something you both agree on. Their statement (much like the one I made to a different person) is that both forms of attraction aren’t (necessarily) a choice by the individual. Their argument isn’t that paedophilia is harmless (your words), but that a person’s inherent brain chemistry and natural development can’t be considered immoral, regardless of context - this would also apply to schizophrenia, sociopathy, various imbalances such as bipolarity, autism and, yes, homosexuality. It is, at worst, amoral, necessitating social help in the cases that do lead to harmful behavior (which don’t apply to e.g. homosexuality/autism, but does to sociopathy or bipolarity).