An atheist perspective does not have God in it...and that makes all the difference my friend. If God is all powerful then He can make His creation pregnant without insemination.
From a Christian perspective, the reason for the immaculate conception is this, Adam, a man, fell …
Atheist know about your beliefs. But Atheist don't believe in God existance. So if there is no god, thinking that Mary cheated and lied about that is a more likely explanation.
If we applied your logic from atheist perspective, Christian beliefs aren't logic and belong in the same cathegory as the "gold rain" that Zeus used to impregnate someone. Or the milk-sea from the Thailand creation myths. Take your pick.
The gospel that you claim is based in historical facts might be very well based on a cheaters lie embellished through time. It is dogma, either you believe it or you don't, but there is no solid proof. And the "witness" might have been influenced by a very charismatic person. After all, we do know that placebo meds work because people is susceptible to selfsuggestion.
Reiki is about healing imposing hands on people.
There are historical records about Troya war, do we have to believe all the stories about greek heroes? I mean, Cassandra could see the future and Aquiles couldn't be wounded except for his talon. So acording bible standards there are "witness" to this "miracles".
But most people think those were embellished stories. Well, atheist and agnostics feel the same way about the bible and your "witness".
So, acording your criteria, we shouldn't respect you. Yet we do anyway. Including letting you have holydays to celebrate miracles we don't believe in. That is what respect means, we let you do your thing, regardless of what we think about it.