There is little point in discussing the teaching of the Church with someone who does not have faith in them. I spare myself the useless exercise. It is indeed true that the scripture does not address the perpetual virginity of Mary other than by inference.
There is no inference. As blue-duncan and forest keeper pointed out there is every evidence to disagree with this teaching. But, to paraphrase your statement, there is little point in discussing the teaching of the scriptures with someone who ...
However, I am always wiling to, like OJ, make a stab or two first.