First off, yes it sucks for the guy who got arrested but honestly with his level of OPSEC, he's either LE or an idiot. It sucks if you lost money, but this is always a possibility, so you should've either not left your money in a DNM wallet, be happy that you can buy drugs online instead of complaining that you lost your funds for your one drug order that failed as opposed to all of the successful ones. If you lost money on a bulk order, you're most likely a dealer and will make the money back anyway.
Moving on, I think it's positive because at least with the info we have so far, LE can't yet hack something like Agora or SR2. They got SR2 because they had something on this inside and the dude used a personal Gmail account. This seizure has got people to more seriously think about a decentralized open source market and a more user friendly version of I2P. As it is now, LE still can't crack our current method of doing things so the fact that these seizures got us developing even more secure methods of free trade means that we will stay a step ahead of LE. By the time they figure out how to crack Agora, we will be using an open source, decentralized marketplace on a network more secure than TOR.
First sentence of second paragraph should be agora and evo, right?