3 Days is a looong loooong time. I don't think minimum holding periods are fair to anyone, at least not above intervals of more than a few seconds. At three days imagine this situation.
On the 1st Joe buys 100 shares of $OIL_COMPANY at $10 a share. On the 3rd Jim buys 100 shares of $OIL_COMPANY for $11 a share. On the night of the third Joe and Jim are sitting at the bar watching the news, and discover $OIL_COMPANY just had a tanker run aground and its probably going to destroy a major fishery, the damages are almost certain to bankrupt $OIL_COMPANY.
Joe should be allowed sell his shares at the open on the fourth leaving Jim and everyone like him holding the bag? Joe has owned the company longer, possibly collected more dividends, paid less for the shares, he should be allowed to keep his profits at the expense of Jim and others like him? even though he and Jim both have the same quality information?
I don't see any justice or stabilizing effect to be gained with such long hold times, it will just discourage investing over all because anyone who makes a new purchase has to take the risk of sitting in a burning building while everyone else heads for the exists, until their hold period expires.
I can see doing trades in baskets of orders entered in say 60 second intervals and processed in random order inside the interval. That prevents a class system where guys with access to HFT have a shot at the getting in or out first all the time and moves it to where anyone with an Internet connection, a E-trade account, and a willingness to sit with three or four of the major news networks on a few tvs has a fair chance of transacting on whatever securities they are playing as quickly as anyone else. That seems okay.