Interacting with executives

The last time I criticized a company executive I was let go shortly thereafter. I wasn't too circumspect with my criticism. So now I am writing something up to offer a suggestion with some implied criticism that will be send to a big-wig. I sent it to my boss to get his ideas on my wording and approach. We already discussed the substance of the message today. I've been kind of spinning this around my head for a week or so and had drafted one message already. Never sent it because carping about such things isn't a good idea. But my boss brought up the general subject and so I let him know my views. He asked me to write it up and send it up to the big wig. Let's just say I'm not particularly looking forward to actually doing this. I'm not afraid to go toe to toe, or to make enemies. But I don't like doing it if I can't see where it'll do any good. And this has a good chance of pissing people off and going nowhere.