The Starbucks CEO should have made his level of support of Israel abundantly clear right from the beginning. A lot of people base their decisions of businesses to support on political reasons. I think had he made his opinion on the issue clear earlier, a lot of people would have boycotted Starbucks but it would have been more fair to his clients.
Being the CEO of a reputable company like Starbucks, it is totally unnecessary and uncalled for him to project his opinion in this manner as it leads to nothing but controversy, which is neither good for his company nor for it's reputation. It is perfectly alright for him to harbor pro-Israeli sentiments but as such, he should keep his feelings to himself.
What a CEO does with his money outside of the company is his own business. Yes, we could boycott his products if we disagree with his political views, but he is a person outside of work and therefore is entitled to his freedom... freedom of speech and money. Starbucks itself is required by law to disclose all financial activities with its profits so there is no problem there.
The current political climate in the Middle East is an issue that even the most educated politicians and delegates have not been able figure out. The issue of military strikes between Israel and Palestine is extremely polarizing, and consumers would have a very difficult time separating a CEO's statement regarding said issue, and the company's stance. Additionally, any statement given by a CEO regarding such a controversial issue, would raise questions among consumers regarding whether or not the business, (in this case, Starbucks), is financing Israel's defense.