It is a Catholic tradition that is not backed by any scripiture or historical evidence. My best guess is that it was used to disregard her relationsip with Jesus in a very male orientated early church culture. Until it got organized and started forming lots of doctrine there were some women leaders and this tradition did not exist.

The prostitute that Jesus kept from getting stoned was not Mary. The Bible does not say it is only Catholic tradition.

If you are arguing tradition talk about that if you want but not if you are talking about the contents of the Bible.

You may now get on with your regularly scheduled discussion.