Go ahead and preach fanaticism. Protestants will happily accept those Roman Catholics who realize Rome is in error on so many things, barrier contraception being only one of them.
Thankfully, the Catholic Church will welcome home all those protestants who see the terrible consequences of artificial contraception. This was precisely the issue that inspired me to leave the Presbyterian church I was confirmed in and convert to the Catholic Church. After researching this issue, I was shocked to discover that nearly all of the protestant denominations had made this dramatic change in doctrine in only a few decades. Unless God Himself abruptly changed His mind, these churches were either wrong before the mid-twentieth century or after. Their moral relativism is apparent in how they twist and distort the clear meaning of scripture in order to place human expediency and convenience above traditional biblical teaching and natural law.
It should also be noted that the problem of contraception, like most other sin's against God's natural law, is ultimately self-correcting. The coming demographic winter of Europe and much of northwestern Asia is sad evidence of the societal poison of artificial contraception. By and large those churches which preach permissiveness toward artificial contraception are already surcoming to a similar fate in their membership. God's divine will can never be ignored for long.