I think the way to overcome it is getting into a better mindset. Remember that no one out there is perfect and that very few people were legitimately amazing on their first try. If you share it on this forum there are fellow devs who will take a look at your demo. They were once a novice and are using their larger body of experience to guide you through their own old mistakes. However, I think it's important to also get feedback from people who are primarily game players. So, passing it to some friends could also be very helpful. But, pick friends you trust to be completely honest with you.
Yes, some people out there are legitimately rude, crude, and unhelpful. Personally, I've found those guys and gals to be far and few between. But, don't let those kinds of people drive you away from seeking out honest feedback (even if honesty stings at times). It is worth its weight in gold.