It's a surprise to plenty of people who think that their $70,000/yr income makes them a net tax payer when it actually doesn't. And it's relevant because people will reduce their marginal income, or relocate to more favorable tax jurisdictions, when the tax burden of that income is excessive.

It's also relevant because, at a certain point, the productive portion of the population will fall below that necessary to make payment on the debt at which point the shit hits the fan in a big way.

70k is in the top ~16% so by your description they are net contributors to the tax base. https://graphics.wsj.com/what-percent/

The cutoff for top 40% is around 40k/year.

PS: Numbers are 5 years old but should be a good ballpark.

According to google te median 2019 household income is $63k. And according to the CBO the median income of the middle quintile of households filing tax returns was $72k. That seems to disagree with your wsj link.

Households can contain multiple people filing separately. Did you mean only 40% of households or 40% of taxpayers?

Anyway, people getting Social Security should really mess with this calculation as someone could be making 150k, but up to 45k of that is from the government.