we could always argue about what the terms "better" and "worse" even mean

Here I disagree. I don't think my values are very different from yours. Making life easier for struggling new parents is something I value. Do you think you have many values (regarding outcomes, not methods) that I do not share?

I believe we differ not so much on values but in our belief on factual matters (which is understandable in politics, as the context is very complex).

For a fact like "The Family and Medical Leave Act makes life better" I believe one should maintain skepticism without good evidence of costs and benefits. A stated purpose of the act is the undeniably desirable goal "to balance the demands of the workplace with the needs of families, to promote the stability and economic security of families, and to promote national interests in preserving family integrity." This no more means the act actually makes life better than a used car salesman's promises mean that the product is a good buy. Same with the CBO; its stated purpose is to advise Congress, this does not mean that it achieves that goal.

Do you have evidence for your belief that this policy "would probably benefit the entire country" (enough to justify the costs and downsides)?