The typical conservative argument I see is that they “already pay the most in taxes,” which may be true in absolute terms, but disguises that they pay less of a portion of their wealth than anyone else.

Call me crazy, but I think the people who benefit most from society should pay more back into it, especially since billionaires get their dragon-horde by exploiting labor.

The article tied to the report is much more informative

https://americansfortaxfairness.org/tax-day-approaches-new-study-finds-u-s-billionaires-now-worth-record-5-8-trillion/
The Tax Cuts Billionaires And Other Wealthy Americans Don’t Need Extended

Below are the parts of the Trump-GOP tax law set to expire at the end of 2025 that exclusively or predominantly benefit the wealthy–including billionaires:

• A cut in the top income-tax rate from 39.6% to 37%;
• A doubling of the estate-tax exemption. In 2024, wealthy couples can shield over $27 million from this curb on dynastic wealth. If this provision is allowed to expire, that figure would drop to the still generous but more reasonable figure of around $14 million in 2026.
• A weakening of the Alternative Minimum Tax (AMT), which is meant to ensure high-income households can’t use excessive deductions and credits to reduce their taxes.
• The ability of non-corporate businesses to subtract 20% of their earnings before figuring their taxes.

The central component of the Trump law was a two-fifths cut in the corporate tax rate, from 35% to 21%. Corporate tax cuts are almost synonymous with tax cuts for the wealthy, because it’s overwhelmingly rich people–prominently including billionaires–who own corporations through their stock holdings. To make the bill look less costly in order to conform to Congressional budget rules, it also included some tightening of rules on corporate tax deductions.

But implementation of these revenue raisers was delayed for several years with the clear expectation on the part of the Republican tax writers and their corporate backers that they would be revoked before ever coming into effect. Surprisingly, preemptive repeal efforts failed and now the GOP goal is to retroactively quash these sensible restrictions on corporate tax dodging.

The recent effective tax hikes on corporations that Republicans want to reverse are:

• Slower depreciation. Businesses write off (“depreciate”) over time the cost of durable items that hold their value like buildings and machinery. Bonus depreciation–which businesses enjoyed until 2023–allows them to instead deduct in the year of purchase the full cost of such big-ticket items, artificially lowering their reported earnings and thus their tax bills.
• Amortizing research costs. Corporate research and experimentation yields benefits that last for years or even decades. So it makes sense for firms to deduct over time (“amortize”) those costs, which they have been required to do since 2022. But big business wants to regain the ability to write off the full cost of research in the year conducted.
• A smaller deduction for interest. Companies are allowed to deduct interest payments from their taxable income, but the Trump tax law restricted that deduction to 30% of a certain calculation of earnings. Until 2022, the calculation that was used resulted in a larger allowable interest deduction. Since then, firms have had to apply that 30% ceiling to a smaller earnings figure, reducing the dollar value of the deduction.

It’s also worth noting that the March '24 Biden budget proposal brings the $400k+ income back up to 39% from Trump’s 37.5$ and tackled a number of other loopholes for the wealthy and included several benefits for the middle class. I’m not able to find what was actually in the approved budget though.

https://www.cnn.com/2023/03/09/politics/2024-budget-joe-biden-explainer/index.html
Here’s what’s in Biden’s budget proposal

Place a minimum tax on billionaires:

• The budget includes a 25% minimum tax on all the income of the wealthiest .01% of Americans, including their appreciated assets. It would hit those with a net worth of more than $100 million. Prior efforts to add this type of tax were not successful.

Increase the corporate tax rate:

• Biden wants to increase the corporate tax rate to 28%, up from the 21% rate set by the GOP tax cut package in 2017. The budget would also reduce incentives for multinational businesses to book profits in low-tax jurisdictions and raise the tax rate on their foreign earnings to 21% from 10.5%. And it would hike the stock buybacks tax enacted last year to 4%, from 1%.

Repealing Trump’s tax cuts for the wealthy:

• Biden’s budget would scrap some tax cuts for certain individuals that were put in place by the Republican’s 2017 tax law.
• Biden’s plan would raise the top tax rate to 39.6% from 37%. This would impact single filers making more than $400,000 a year and married couples making more than $450,000 per year, according to the administration.
• It also proposes taxing capital gains at the same rate as wage income for those earning more than $1 million, as well as closing the carried interest loophole that allows investment managers to treat much of their compensation as capital gains – thus lowering their tax rate.

Nothing will fundamentally change

-Joe Biden to billionaires in 2019