How exactly is not having this extremely speculative stock and currency trading running at the timespan of milliseconds became 'having to do everything for themselves'? Or are we speaking of the market where i buy groceries?
Both are parts of one continuum. Somewhere in the middle is e.g. a possibility of making billions by creating Google.
A proper tax can make a part of this continuum mostly unprofitable. We just better be careful not to remove unnecessarily big part. Good luck finding a rational solution for such politically charged topic!
The last point reminded me of speculation from the recent LessWrong article Conspiracy Theories as Agency Fictions:
Before thinking about these points and debating them I strongly recommend you read the full article.