Well, I think the government ought to eliminate capital gains tax if you hold stock for 5 years or more
Can't really disagree with that notion, but I doubt it would be that simple. The problem of course is the unintended consequences. Capital gains are charged to home owners who sell and to entrepreneurs who work through their own S-corp or C-corp companies. Now you have to write individual exclusions for all the new avenues of tax avoidance that have been created.
Invest your money into houses, hold for 5 years, flip and re-buy without paying any taxes on the gains.
Work through your own S-corp, take no payroll for yourself, leave all the gains in the company and after 5 years you can take it all home tax free.
There are many more examples, plus there will be all the new 5-year schemes that will be created just to avoid taxes on investment income. That's a lot of special situations, exclusions, and careful wording that would have to be created just to support what is initially a simple idea.
It could also have a counter-effect. People may have legitimate reason to do what they're doing, and if you remove the incentive to do it on Wall Street they could move their large sums of money elsewhere in order to continue their current behavior. Wall Street collapses and something else pops up to absorb big-time, short-term money activity.
There simply are no easy answers to what is a very complicated situation. Even the simplest of interventions can have wildly unpredictable results.