This is a very odd disclaimer. It almost seems like a reasonable warning at first glance, and I think some people actually believe in what they're asking when they make it, but if you break it down into it's meaning and intent I don't think it's so innocuous. In fact, I think this is one of the most awfully passive-aggressive statements commonly repeated among people of otherwise sound judgement.
Who self-identifies as easily offended? Nobody.
What you are asking really isn't that people do not read. There is no set of people that identifies with the warning and this is understood when the statement is made. Neither are you asking for forgiveness for whatever distasteful communication is to follow. You are, in reality, prejudicing your reader, viewer, or listener on the basis if they have a problem with whatever offensive material follows then it is because of a flaw in their own character. You're redirecting the blame for your own offensive opinion onto any more reasonable person who may see it for what it actually is. How can you be accountable for your own bigotry if they chose to be offended?
It's also true that your audience doesn't owe you an education. It isn't their responsibility to shoulder the task of pointing out why your opinion is offensive. They don't owe you a debate, especially given the prejudiced initiation of your statement. You've created an environment in which any disagreement is already hostile because you presumed that you were both correct and that any dissent was a weakness. Your opinion, therefore, will likely go unchallenged — but this shouldn't be mistaken for justification.
The fact of the matter is that you are being intentionally offensive. Wilfully offensive. Your disclaimer is in essence a threat. The next time you feel the need to preface your comments with some stipulation that attempts to negate discussion you should probably critically examine the belief you are about to share. It would seem that you already recognise that it is flawed.