Do you believe that you are able to influence the big company's practices?
That's not what you asked. You don't send hate mail to politicians, or corporations. You inform politicians you are a voter, express your dislike, and make them understand that you will not support them in the future, and will try to gather support from other voters to vote for their opponent.....you write a company, and express dislike for policy, product, or practices, and inform them you will not patronize, or purchase from them anymore, and in some cases, you will go on a campaign to get others to join your crusade.
You send hate mail to an individual person.