Why do some conservatives and libertarians want some Americans to pay more in taxes?

Oh, they don't actually come out and say that. Then they would sound like Bernie Sanders or Hillary Clinton.

What they do say is that certain tax deductions are "loopholes" that need to be "closed" because they "distort" the tax code, "subsidize" high-income taxpayers, and encourage people to make "economically unwise decisions." Although most of them also add that the increased government revenue that would result from the elimination of a particular deduction should be used to "pay" for "good tax reform" by "offsetting" the "cost" of lowering tax rates and making the tax code "simpler" and "fairer," there is no getting around the fact that some conservatives and libertarians still want certain Americans to pay more in taxes.

The latest deduction under attack is the State and Local Tax Deduction (the SALT deduction).

Let me first explain how tax deductions work and how eliminating them, reducing their value, or phasing them out above a particular income level is no different from raising tax rates.

Tax deductions serve to reduce one's income subject to tax. Taxpayers will pay less in taxes the greater the number, and the higher the amount, of deductions they qualify for. All taxpayers can generally claim a standard deduction of $6,350 ($12,700 for married filing jointly). Many taxpayers can also claim deductions for educator expenses, business expenses of performing artists, health savings account contributions, alimony paid, moving expenses, the deductible part of self-employment tax paid, health insurance premiums paid by the self-employed, IRA contributions, tuition and fees paid, and student loan interest. Instead of taking the standard deduction, some taxpayers can itemize their deductions and end up with a larger total tax deduction. In this case, allowable deductions include medical and dental expenses, state and local taxes paid, real estate taxes paid, home mortgage interest, mortgage insurance premiums, charitable contributions, casualty or theft losses, unreimbursed employee expenses, and tax preparation fees.