Main purpose of a corporation

When should a company respond to pressure from stakeholder groups, particularly when they are raising moral questions? How much power should companies give to “non-market” stakeholders (e.g. NGOs) to shape and inform their decisions? What is the best way of engaging with groups like this? Can decisions ever be justified on the basis that other companies would behave less responsibly? What is the main purpose of a corporation: shareholder or stakeholder value?