In your opinion what are the reasons that let someone start dumping his bitcoins and walk away ?
I personally (and this is just my opinion) that it's more panic then simply his need of money or something else , as we saw on the BitcoinXT last time , people started to panic and simply sold their bitcoins and that caused a drop in the price .
here are different categories of people, some people (like me) use it just as a currency, I buy it, spend it then buy again, the price of it rarely bothers me, since it's pretty stable for sometime now with minor ups and downs. Then there are people who buy it as an investment and to answer your question, they dump it because maybe they made their profit and will buy again when the price drops or they lost some money and they don't think it's safe to keep on holding them anymore but for whatever reason someone dumps bitcoin it's really up to them what they do with their own money and I say let's not judge them and call them names, time will tell if they were losers or winners.