My recollection of that time was not that doctors recommended being exposed to chickenpox but rather that parents sometimes chose to expose their children at a time they felt might be more convenient for the family, since everyone would catch it eventually. Some recommended times to get it: while you only had one child to look after (subsequent children then each getting it one at a time), while it was summer and they could play outside without clothes that might hurt on rashed skin, before they started school so they wouldn't miss class time, and so on.
When the vaccine was new, there was uncertainty about how long the immunity lasted. My doctor recommended at that time that if a girl didn't get it by puberty, she should get the vaccine (chickenpox while you're pregnant is serious.) I believe the current recommendations are to get the vaccine and try to avoid catching the virus, which thanks to the vaccine is a strategy you can actually follow, since less kids now catch it.
Wikipedia says doctors have never recommended deliberately getting infected with anything, and it seems pretty easy for reporters doing a story on such parties to find a doctor who says it's a bad idea.