That's not true. Here's just one example: fine-grained taxes are used to help influence behavior, improving public health. Mexico increased taxes on sugar [0], with the result being a fall in consumption. Raising this tax has caused a verifiable reduction in consumption, which has a direct impact on public health[1]. That's just one example, many more exist for all sorts of reasons. It's why cigarettes and alcohol are taxed differently than broccoli. Obviously not all taxes are in the public interest, but neither are they just to give some government official a feeling of empowerment.
[0] https://www.theguardian.com/society/2017/feb/22/mexico-sugar...
[1] http://journals.plos.org/plosone/article?id=10.1371/journal....