Oh, I'm sorry to hear that! I wouldn't feel too bad about it though, after all you are having a AHR and are letting people know that they can come if they want to. I would assume that your friends should know you and know that this is what you want and makes you happy - they should be rooting for your happiness and stop being so selfish. Just my opinion! The wedding is about you, not them. And to me it does sound like you are having a real wedding - just one without the added fluff.
In our case the tension came from inviting people who in turn couldn't afford it - it was more a "I dare you get married in Mexico, it's so expensive". Like you said, you can't please everyone! So just ignore their comments and stick to what will make the two of you happy. In the end, that's all that matters.
Good luck!
PS. My sister-in-law told people that she was having a "just very close, immediate family" wedding as her reason to not invite everyone, and people let her be. I think when you exclude everyone instead of just some people, it makes it easier for people to understand and not take it personally.