Suppose in a listed company, the promoter owns more than 51% of shares. In that case, what prevents the promoter from exerting his own free will, like appointing his own family/friends in important positions and siphoning off profits in the name of taking salaries and commissions.
Even the collective votes of minority shareholders will not matter as the promoter owns more than 51% and his vote will ultimately overrule.
"What prevents abuse by majority shareholders?"
Most jurisdictions have laws that attempt to protect the rights of minority shareholders. The basic principle would be that the majority shareholders cannot intentionally reduce value of the company / reduce value attributable to minority shareholders.
Whether those laws are sufficiently comprehensive, or enforced, or effective, would probably be a few phd-theses-worth of material to discuss. In particular, the country you're in will affect the applicable laws and their outcomes.
