How so? I understand markets go up and down and would love to understand to origin of such a bleak opinion.
Look at it like this: Let's say the price (in dollars) of a real estate property we have invested in doubles in one year. So we should be doing pretty good if we flip it, right? Well, not if we invested bitcoin, the price of which (again, in dollars) quadrupled in a year. if we flip this house, we'll actually lose money.
Then there's the empirical approach -- how is the market doin'? Well, if we take Havelock exchange, which is doing pretty good by virtue of it still not being shut down/getting "hacked" *cough*, you will see that every "security" listed there is trading below IPO.
This doesn't mean you can't do some clever trading, but you have to be ... well, you wouldn't be asking.
If you believe in bitcoin -- buy, hold, and get rich. Forget securities.