Firstly, I would like to say that we need to respect their opinions.
Not all of them are wrong but they should be told that they can not judge a person just because he/she is using this currency. There are those who just use bitcoins to scam while those who are genuinely USING this currency for their
business or other legal activities.
Like you said bitcoin ecosystem also has two possible sides. There are ponzis using this currency but there are also genuine trading websites using it. We can not ignore based on one side alone.
Yeah every coin has two sides, one is good other is bad, you need be really smart before making any investments into it or else you will regret for sure.