For example, the states that thought they'd pay for their health care systems by increasing the taxes on cigarettes have learned that increased price per pack has resulted in a decrease in revenue as more people stop smoking. Increasing the gas taxes will cause less use and less tax revenue, so it will be harder to pay for the things the gas tax is intended to pay for.
Shocked you're modded insightful when you seem to have overlooked the obvious point that the idea is to reduce consumption, which will help attain reductions in costs of managing smoking/gas externalities. Also overall revenues will not necessarily go down, certainly in the case of gas tax. Typical Libertarian logic fail.