You should qualify that with the word "yet". Is there anything in Litecoin's design that doesn't allow it to be used for drugs and by black markets? No. Honestly, Litecoin doesn't even have that going for it. Acceptance as an actual currency is the difference between a cryptocurrency becoming a legitimate investment versus a speculative pump-and-dump scheme.
I assume that mining will tend to be modestly profitable. As Bitcoin scales up and as the reward goes down, either it will have to increase transaction fees and use an enormous amount of energy, or the mining reward will be too low compared to Bitcoin's value, there won't be enough miners, and 51% attacks will start to be profitable.
This isn't a problem for PPcoin, which gradually transitions to proof-of-stake instead of proof-of-work. It seems to me like it'd be more viable as a major currency.
There's also PPcoin a low energy coin compatible with BTC miners that's getting more popular.
Another advantage to Litecoin is you don't see it in the news everyday with the words 'Drugs' and 'Blackmarket' beside it, meaning correspondent banks will still deal with you if you want to set up an exchange whereas a lot of banks now are dumping bitcoin startups out of paranoia