Why not abolish marriage certificates for everyone?

[Tiberius]

Tiberius, raising a child engenders more risk and a significant drain on resources, even when multiple people pool them.

The societal view is that we give subsidies to families (which are more likely to have planned children) to equalize their risk to be competitive with individuals.

I don't think you quite followed my post.

You asserted that Libertarians don't say stuff like "let's minimize the differences between X and Y so we may consider removing something" but rather prefer to say "Remove X" or "Abolish Y". I was countering that my post was more of the former and less of the latter. That I didn't say to abolish or remove benefits outright, but rather thought that some specific aspects were unfair, whilst other aspects were definitely needed.

It is understandable that children are expensive, and a significant drain on resources, but my major point of contention is not with benefits for children, but with benefits for couples "just because" they are married. Take, for instance, the Married Couples Allowance in the UK: https://www.gov.uk/married-couples-allowance/overview

Effectively, it's a tax cut for married people...just because they are married. I think that's unfair on single people. Note that this allowance is given even if the couple don't have children / aren't planning on having children. It has nothing to do with children.