Some of the things the Duggars are into are not well known. Too much to explain here, but anyone who is interested can google "Bill Gothard" "IBLP" "Visionary Daughters" "Quiverfull" "Vision Forum". There is a lot more behind it than just a personal decision to not use birth control. One guy who is the brother-in-law of their oldest son who got married, has defected from the movement, although still a Christian. He has a blog called IBLP detox"
I was exposed to the Bill Gothard seminar in my late teens - he uses Bible verses in much the same way as the Watchtower, almost all completely out of context. His stuff is extremely filled with extra-biblical rules, odd applications and legalism. It seems to have an appeal for parents who have fears for their teenage kids. Extremely patriarchal - girls should not leave home until married, not go to college, etc.