The Qur'an says trade is allowed, halal, and adding money on top of money, interest, riba, is not allowed, haram.
Bearing this in mind we may judge whether an exchange of money for shares in a company for the express reason of making gains out of someone else's loss is allowed or not. Best opinion is haram.
Pros and cons applies to every activity as a thief gains something from their activities but it does not make it halal.
If you were to drive a car without having proper driving lessons, recklessly killing people every day, then this would be stupid, but driving with a valid license, with care and knowing that it is potentially dangerous is not the same.
There is something called consensus in Islam which allows forum members to express their opinion.