Maximilian, I share this question with Black Elk. I'd really like to know, so I can have a background on your point of view.
I hate to duck such a good question, but it's a big issue, and I simply don't have time today to write something. Hopefully I'll find time tomorrow.
I have written extensively on this topic numerous times here on FR. It's unfortunate that the search engine is so notoriously poor. But if you were able to do a search through Google or something, you might be able to find some of the pieces I've written here on FR in the past that explain why Humanae Vitae was the death blow to the traditional Catholic view of marriage.