OE

If “the government is rightly interested in curtailing” the use of a product, this suggests that the product is somehow harmful, or of a “noxious” nature, so that’s the first blank. Both “salubrious” (healthful) and “solicitous” (expressing concern) are positive words. By taxing such products, the government gains a profit from their consumption. That the government is “threading a thin line” suggests that there is a conflict: on the one hand, the government has an interest in increasing profits, and on the other hand, it has an interest in curtailing the use of the taxed substance. So the problem is that the taxation provides a reason to encourage, or “incentivize,” use of the product. This taxation would neither “legitimize” nor “signify” government support for this product consumption