Yes it's purpose is for good. As you can see on the platform of btc, what their goal is to use btc in digital currency, easiest and secured mode of payment. However, bitcoin can be used for bad things. It is depend on the people who use it.
I agree with your statement just like with our regular fiat money. Spending it for good is a choice from someone who owns it. We ca not deny that there are also who are using bitcoin for illegal activities and fraud.