The problem is not denatured alcohol but that it is not always clear what it is denatured with and the consumer grades may be contaminated with rather unsavory things at least as far as cleaning applications. I have had problems with consumer grade isopropyl alcohol as well where it left film or deposits behind. Taxed alcohol at least has the advantage of being suitable for consumption (I hope!) and therefor being "food grade" so it will not have kerosene, MEK, or benzine in it.