Governments run on taxes, and if they don't receive enough revenue via taxation, they run up deficits, and while there are not a lot of people that enjoy or appreciate being taxed, the bottom line is that in order to have a functioning government taxes are imposed. It certainly makes a whole lot of sense to tax people where the money is at, with Wikipedia.org indicating that the "… average daily trading value was approximately US$169 billion in 2013," for stock trades in America, this would strongly imply that imposing a reasonable sales tax upon stock transactions would have its place, as currently while buying and selling of stocks in America, consumers of such are only subject to a commission and a fairly innocuous regulatory transaction fee which in almost all cases is even lower than the commission to make the trade in the first place.
The thing is, when you purchase a car, you pay a sales tax, when you purchase household items, you pay a sales tax, so it isn't any real stretch to believe that when you purchase a stock, the person or entity doing so, should be subject to a small sales tax. When it comes to establishing such a sales tax, it seems fairer to impose it only on the initial buy of the security and not on its sale, which would serve the dual purpose of reducing somewhat the rapid trading in and out of securities, as well as impressing upon people, that an investment should be more about making a decision and holding onto it, as opposed to the higher volatility of hyperactive trading.
There isn't any necessary reason why the proposed sales tax should be equally applied to all, since, in fact, the income tax is progressive in nature, and in consideration of the fact that equity and bond investments are a real source of passive income to those that have considerable assets, the sales tax should only be imposed for those buying stock investments that exceed perhaps $50,000 in any one trade, in which the sales tax begins at the $50,000 number and above, with the additional component of having a sales tax "wash rule" so that those buying the same stock or security within 30 days in which in aggregate the total buying of that security is greater than $50,000 would be subject to that sales tax.
Wall Street is an incredibly powerful force in America, and no doubt, wouldn't see any benefit to such a sales tax, but one must also keep in mind that Wall Street is currently subject to capital gains taxes, and carries on just fine, signifying that if the sales tax was low enough to generate good tax revenue but not so high as to spoil the stew, than all would continue to be well, with the additional benefit of tax revenues so generated.
Most assuredly, there are seasoned economists that could take a look at the numbers and determine what price-point would be most effective in producing tax revenue without unnecessarily interrupting the business as usual crowd with Wall Street, especially considering that the dollar volume of trading being so high, that one would think the sales tax percentage proposed wouldn't need to be much higher than somewhere in the range of .10% to .25% to generate tax revenues of real meaning from those that obviously have the money and the means to pay their fair share.