A forum only concerned with economics.
Bitcoin is the basic currency used on the dark web also, right? Not that I have ever been there. I can buy $100 of bitcoin (0.01389 of a bit at $7,200?) and buy stuff.
Like all currency, there is always a dark web involved somewhere, like the American dollar being used to fund prostitution, illegal drug deals and other black market products.
I don't know if you remember what happened a few months ago where some hackers attacked companies around the world and kept their information ransom through the wannacry virus software. They requested to be paid in Bitcoin as it is less likely to be traced than the other currency. So yes, there is always risk involve.
I am not entirely aware if you would be able to buy a certain portion of a bitcoin or if it is only priced at a full coin.