Aside from some long dead theologians stating that Onan sinned by not raising up a son for his dead brother, they cite no Biblical support for the position you maintain.
Wrong.
All of Christianity for 2000 years has been unanimous on this. A very small minority of 20th century "christians" have adopted a diametrically opposed interpretation.
Yet those "christians" look back on all the Christians that preceded them mockingly, and state they were all wrong while we enlightened 20th century christians are right.
Most wise Christians would realize their views are diametrically opposed to the entire witness of 2000 years of Christianity, and reevaluate their own views, not mock the continual, unanimous universal teaching of all of Christianity for all time on this issue.
This is the textbook example of worldly wisdom of men opposed to the Wisdom of God.
But modern non Catholic, non Orthodox Christians have fallen so far into heresy on this, you probably, hopefully, are not culpable.