I know alt-coin supporters and specifically Monero supporters are ecstatic over a wiggle in their value, but there are larger problems such visibility raises. Without getting into technical details, lets just focus on the collective hashpower of the Monero network.

http://minexmr.com/pools.html

There's a graph near the bottom that shows the average collective hashing power of the major pools - 24.1 Megahashes/sec. This is a laughable minority, which brings to fore another potential threat. Lets say you're law enforcement or some other actor. All of these people doing things you perceive as illegal have adopted a poorly-defended alt-coin as their method of trade (Citation needed - extremely dubious).

So, as a LEO you work on how to disrupt this network.

If this was Bitcoin, well, you have a lot of work to do if you're trying to be a majority miner and make your chain the "correct" one. Bitcoin's collective hashpower stands at an estimated 1,798,050 Terahashes/sec, magnitudes higher than a paltry 24.1 that Monero offers.

Guess which is easier to attack?

The point is, I'm extremely doubtful that anyone would jump on the Monero train and not have their network severely disrupted by law enforcement if it indeed became the "currency of the darknet". Its simply too small and too poorly secured.