The stock market has a number of essential components without which it could not exist, all of which support it's role in allocating capital. If there was no secondary market to sell their stock to, someome might not invest in the first place. If there were or were not market manipulators cheating others out of money, that would make no difference as to whether someone invested in a company.

Secondary trading enables risk transfer, which is important for allocating capital.

Your first sentence is somewhat accurate, your second is not at all, specifically "just".

I didn't say stock markets don't serve a useful purpose. Regardless, my original point is simply that traders should focus on fundamental value, not try to guess what others are thinking. If they choose to play that game and get burned, that should be on them. There's no real necessity to regulate "market manipulation".