Insider trading being illegal encourages participation in markets for people outside the company. As well as discourages intentionally messing up within the company and profiting from short selling
The argument against it is that markets would be more efficient if people were allowed to trade on information not yet available to the public
The argument against it is that markets would be more efficient if people were allowed to trade on information not yet available to the public
Seems like a worthy tradeoff to me