As to your other question, if you raise the cost of a transaction, you haven't prevented the value of the asset from changing, you've only raised the threshold that short term traders need to make a profit. If a bid offer spread is .1 and a .1 tax is added to each transaction, the spread will change quickly to .15 or so depending on how the market organically decides to address the disposition of the tax. So now instead of each change in price being between the bid offer spread being .1 points apart, They will be .15 points apart...which is more volatile than before.
This concept translates into longer time frames as well, but it's a little more complicated to explain. The cumulative cost of information is a big part of why 2 different people can look at the same asset at the same time with the same information and think it should have 2 different values. If you increase the cost of information, you increase only that difference. In the end, that difference of opinion, or lack of consensus is what leads to volatility.
I don't mean to imply that it's a phenomenon with a single cause because it isn't. Many things effect the change in consensus strength at a particular time, but it's certainly a contributor.
the best thing to do to reduce volatility is to find a way to make the markets more efficient. Adding a tax does the opposite.