That would mean an end to the misnamed 'capital gains' tax.
There is one conservative principle which states that the government shouldn't pick winners and losers. One of the ways that the government tries to do this is by taxing different activities at different rates. If we believe in this conservative principle then there should be no difference between 'capital gains' and wages.
Another conservative principle is that the government shouldn't try to do social engineering with the tax code. Taxing 'capital gains' less than wages is a form of social engineering, i.e. encourages more people to be investors and fewer people to be wage earners.
Another conservative principle is that we shouldn't lie to ourselves. The vast majority of trades have nothing to do with 'investment' in the way economists mean when they talk about 'investing in our future', 'investing in our infrastructure', or 'investing in technology', etc. If we really want to violate the other two conservative principles then we should regulate trades in such a way that we can clearly demarcate true investments from mere speculation. Then we can favor investment over rent-collecting, wage-earning, etc.
Of course we can always throw principle to the wind and be the sort of conservatives that are merely 'pragmatic'. We can look at past history and say that every time something we mischaracterized as a 'capital gains' tax is lowered, the economy booms. But becoming out-and-out pragmatists has its downsides. After all, it is often the 'pragmatic' thing for individuals or businesses to take their profits and use them to lobby government officials rather than invest in R&D, etc. Free market theory suggests that in the long run such rent seeking will ultimately lose out to companies that compete on price, service, and quality of goods.
However when I look at the long run I just see more and more companies acting pragmatically in their own interests directly and indirectly creating an ever-expanding tax code and regulatory environment to the detriment of the economy as a whole.
I agree with you on the not picking winners and losers and not doing social engineering.
But I disagree with you on the “lying to ourselves” bit.
Even under the current tax code, people who trade securities as a business (whom you would no doubt consider speculators) pay tax on their income/loss at ordinary rates either by marking-to-market or as short-term capital gains.
But people who take earnings that have already been taxed and place that money with a long term holding period in an investment are not speculators.