“Im sure you havent but I presume (based on your posts) that you did not grow up in an insular little box the way many yeshivish people nowadays do. Its very different for someone who grew up open minded in a setting where its accepted to speak with people of the opposite gender, than it is for a couple who never dealt with anyone from the opposite gender besides their spouse. For them it is much more dangerous”
You are absolutely right. That is pretty much what it comes down to. I, personally, would have no problem having young couples over because I grew up among people who would, and where it is considered normal to be sociable with the opposite sex. Therefore, I find it totally fine to have any type of guest over. But in more “Yeshivish” circles, where it is considered wrong to be sociable with the opposite sex, it may be more prone to lead to problems if they have young married couples over, since they aren’t used to such a setting and wouldn’t necessarily know how to act and where to draw the line.