S3TC analysis, page-12

It doesn't matter what taxation legislation you put in place, people's personal circumstances will always make it impossible to please everyone.

For a long time single people have been penalised for not being married & having kids. Single people are basically contributing to other people raising their kids either through direct measures like taxation & benefits or indirectly via education & health.
If parents had to pay 100% of the costs of raising their own family then significant number wouldn't be able to afford to.

Of course there are the intangible benefits of contributing to paying to raise other people's kids such as a better educated society, providing services to you when you are sick/old etc.

But it would be nice to hear some gratitude from the parents of these families!