News flash: Prefacing an offensive statement with the phrase: "no offense" does not thereby render the statement inoffensive.
Examples of proper and improper usage of the phrase "no offense":
"No offense, but I don't really care for onions." (Unless the line is being delivered to say, perhaps someone who makes his or her living as an onion grower).
"No offense, but I don't support gay rights."
Now, with regard to the second example, of course certain people won't be offended by it one bit because they feel the same way. But those people don't need you to say "no offense." The people who will be offended by it though are the people who think that gays have as much right to live their lives and be happy as do heterosexuals. And for them, prefacing the statement with the words "no offense" is about as effective as, oh say telling an African American, "No offense, but I don't support desegregation."
If a person is gay, or has gay children, or siblings or friends whom they love or whom they care about very much, and you tell them that you don't believe such people should have rights, well it pretty much doesn't matter if you coat that opinion in chocolate and sugar, spray it with essence of lilac and wrap it in money... it is going to be offensive.