Really? Jesus had to have siblings to improve His character? I thought I have heard everything...
What's so wrong about sex between a husband and wife that Mary couldn't have done
Nothing. She could have had marital relations with Joseph if she and he wished to. It is by the way about the fifths time someone asks me that question. Can we consider it answered by now? That Mary remained virgin all her life is a historical fact known by the Church. It is not some kind of malleable story that the Church writes every way she wishes. It happens to be fact. Thanks to that, there was no detractors trying to say that Jesus was simply an illegitimate son of some unknown father, or a son of Joseph conceived prior to marriage. So it is a very fortunate fact for us, Christians.
That Mary remained virgin all her life is a historical fallacy made up by the Church.
It can NEVER be proved. Only presumed.