How is it better to not be legally barred from office but effectively barred from office when people find dirt on you from back then? What is the big difference? You can see the effect: At some point, people stop caring completely about decency.
Because these dirt stories get thrown around so often that you just believe what you want to believe. Which is why people like Trump can win if they just ignore all the skeletons in their closet.
With logic like that, you also invite stuff like Obamagate and, on the flipside, personal stories over policy like 'i was that girl'.
Because you put emphasis on narratives that frame a politician in a certain light independent of his policy proposals instead of far more relevant questions like experience, public record and his proposals.
Without knowing what exactly he did (so no details), how would that even matter? What you expect from him is that he goes on stage, without anyone asking, and saying 'by the way I'm a rapist'. That is not rational. That would not make him a better or worse man, it would not make him a better or worse politician, it would just end his career.
The only way out would be, as you outline, to make it his story 'Hey, i did some bad shit in my past but i worked beyond this, vote me now, give an ex offender a chance!". That is really cynical to me, and again is a push for politicians being more narrative than actual person and narratives mattering more than actual policies.