Is Mary's virginity evidence that sex is always sinful? It seems that sex is always a sin, as evidenced by the fact that Jesus had to be born of a virgin and not by traditional conception in order to be sinless. Is this true?

Any viewpoint is welcome.
No no, it's not a sin. It could easily become a sin if we pervert that which was intended for good.

I believe that Mary's virgin Birth was a testification to the Truth of Christ. Could you imagine what the Catholic church would have done with the Husband? "Father of God" I'm sure that would have been completely chaotic. Who's really the father of God?

Well, we know through the virgin birth that only God the Father is the Father of Jesus Christ.