If the companies value and ambition is to maximize the stock price then the stock price is a good metric. If the companies value is something else then stock price isn't really a good metric.
It will also attract shareholders that share those values and thus going against them will cause an uproar.
It really depends on their charter. People don't park money in a company simply to have the stock value drop or stay the same -- with exception of companies who pay out dividends.
Most companies charters talk about their relationship and obligations to the shareholders -- people don't invest in companies that don't intend on increasing in value.
Again, value doesn't have to be monetary. Shareholders has the right to expect return on their investment, yes. If the company delivers on their ambitions and values then that is the shareholders reward.
It will also attract shareholders that share those values and thus going against them will cause an uproar.