The assertion being people who want to have threesomes are less likely to have children?

I suppose that could be the case, however I am fairly unconvinced that this has any real affect on the population in comparison to the cost of having a child coupled with the rise of understanding the costs involved with having a child.

I am curious... Why do you think so?

The app is promoting and is a manifestation of what a National Review essays calls our

Our Childless, Childish Culture By MADELEINE KEARNS August 8, 2019 3:34 PM https://www.nationalreview.com/2019/08/our-childless-childis...

In the Western world and Asia, fertility is below replacement world, and in the Western world, the fraction of children born out of wedlock, who do worse than children of married couples by any measure, is rising. So I think working on something like eHarmony is much more moral than the app discussed in this thread.