Overall, I think you're making a lot of assumptions here. I actually watch 19 Kids and Counting. Originally for the WTF factor and then because they seem like a genuinely kind family and I've gotten to know families like theirs through volunteer work. While you may disagree with chastity before marriage or their conservative way of life, that doesn't make it inherently wrong or unhealthy.
the way the parents handle sex, dating, and intimacy with their kids
On tv. Michele has been pretty open about the things they hold private. The very fact that they are so conservative should give you a clue that they are not going to put such intimate discussions on tv.
When their children date, they are never allowed to be alone together. Every date must be accompanied by a chaperone, even if they are in public.
Chaperones are common in a lot of cultures. When Jill was in Nepal and being 'courted' by her now-husband, JimBob definitely gave them space and wasn't a constant hovering nightmare. And I thought the way that Jill and JimBob discussed the courtship and their compatibility was very open and mature.
And for the one's who have gotten married, they all save their first kiss for the wedding day. A fucking KISS.
It was very clear that for Jessa, saving the first kiss for immediately after the ceremony (in private) was their choice. It was meaningful to them and it doesn't seem right for you to judge the importance of a physical act to someone else. The whole series leading up to the wedding, JimBob and Michele took every opportunity to embarrass the couple by kissing saying they were "showing them how it was done". I thought it was cute.
All of the children who are married went through marriage counseling before the wedding which Jessa disclosed includes discussion of sex and that sexual intimacy is an integral part of marriage.
When you don't have appropriate conversations with your kids about sex
How do you know they didn't/don't? I may not make the same choices that they did, but it's obvious they take marriage very seriously. And Michele has written articles and given interviews on the importance of sex and physical comfort in a marriage. Having known a lot of conservative Christians (being an Atheist myself), believing that intimacy before marriage is sinful does NOT mean that they have an unhealthy attitude about sex or don't find it pleasurable for it's own sake. There are a lot of really repressed families out there of all religions and inclinations, but many conservative people have very healthy and enjoyable sex lives and many of them (believe it or not) have very open and healthy discussions about sex with their children in order to prepare them for sexual intimacy after marriage.