Shareholder loyalty
Just as management should manage their investments for their personal best interests, shareholders should invest or sell based on their financial situation. I thought that was obvious, but I'll expand a bit to be clear, since it appears my hypothetical response somehow was interpreted to include a call for shareholder loyalty.
Loyalty to a stock is completely illogical to me. Anyone who thinks shareholders should be loyal to a stock are nuts. Stock is in investment to make money. You should buy it/hold it when your expectations for it fit in to your investment strategy. The minute it no longer fits, you should sell.
To summerize, management's responsibility is to manage the company to the best of their ability for long term success. Investors, whether insiders, institutions, individuals or anyone else, should invest to maximize their own financial situation within the letter and spirit of applicable laws and regulations.