I don't think this is why we have income tax. All taxes are artificial. They're artificial rules inserted into the natural market, like how we put a bit into a horse's mouth so we can influence it's behaviour. I think the better question for any tax is: are we putting the bit into the horse's ass? It seems to me this proposal to tax bandwidth was more like that; it's just bad policy.
Capital is taxed in small number of countries (which is in my opinion unfortunate). However, most countries tax capital income, and if one agrees that taxing regular personal income makes sense, one should also tax capital income.
I don't see this as logical, because agreeing that it makes sense has nothing to do with whether it's effective or not.
Taxing capital gains reduces the amount that can be allocated into generating new wealth, which may mean lower overall tax income in the long term. I'm not saying we have it right, but that it's really very complicated.
This is really true of all taxes. The tax money comes out of someone's pocket and that person may have otherwise invested the money or done some other economically productive thing with it.
So does taxing any other form of income. Preferentially low taxes on capital gains favors wealth accumulation by people who already derive income from capital and, at any given present revenue level, relatively disfavors wealth accumulation by people who derive income through means which are more heavily taxed, notably labor income.