Of course, Bitcoin is a currency, Therefore it's being used for illegal activity and that's a given, even USD is being used for illegal activity as well as any currency in the world... The fault is on the one using it for illegal activity not the currency.
Correct the currency does not have some kind of magical power in order to determine if the trade its being used is legal or illegal so its the responsibility of the user.
Yes it depends on the user on how he is going to use bitcoin, for good or for bad things. Since many people are already into bitcoins. We can't deny the fact that it is being used for different illegal activities. Since bitcoin is anonymous, the people who are doing that are taking advantage for using it since their information are not included per transaction.
Everything comes down to the intent of the user. Users of Bitcoin, silver, gold, US Dollars, whatever it may be, can be using their medium of choice to do legal or illegal activities with it. Nothing really stops them from doing it, the law only stops them when they get caught. That's it. If there is a will there is a way.
Agree that it is always depend on the users if they want to use it in illegal we can not please them not to do because we are all have freedom to used bitcoin what ever where we want to used it.