Ok, I'll give it a shot...
According to the FAQ, the main reason flat earth proponents believe the earth is flat is that it "looks that way". I understand there are some (questionable) experiments to further back up the idea, but I'll assume these are merely supportive, and that the main reason flat earth proponents believe what they do is their personal observation.
So I'll ask this: If you assumed, for the sake of argument, that the earth was indeed round, then, following your logic, the earth would indeed not look flat from your local reference point. If it did, then both theories would be equal on that particular point, weakening your theory. Hence you might want to present factual evidence to the rest of us, that, if, hypothetically speaking, the earth was round, it would actually look different to us than it does. Since you acknowledge gravity, you can't argue we'd fall off. Since the hypothetical assumption should also include the earth's large radius, by mathematical considerations it wouldn't look "bent" to us from down here. So what exactly would be the observable difference in this hypothetical world that cannot be reconciled with your actual observations?
Remember, bogus experiments will not answer this question, since this would mean you admit that from your personal observations, the earth "might as well be round" and that only those experiments show otherwise. So the flat earth theory would merely be a strong trust in the validity of a few bogus experiments, combined with a strong distrust in the validity of a much greater number of other experiments. This is obviously much weaker than a theory which claims to match universal personal observations while others don't. So choose wisely whether or not you take that step.
Of course you might take the position that your personal observations lead you to tend towards flatness, and that while a round earth would lead you to have the same observations, it seems more complex to you, and, denying all evidence to the contrary, you will stick to your personal impression.
Here's a few examples which illustrate this line of thinking:
- (About a person in a coma) He looks dead to me, so I'm going to assume he is and bury him until someone proves me otherwise. Breathing? Must be an inflating balloon in his chest, since, after all, I can see he's dead.
- (About an alleged serial killer) He looks guilty to me, so I'm going to assume he is and lock him up until someone proves me otherwise. The butler already admitted to it? He must be lying, since the defendant looks guilty.
- (About a person with internal bleeding) He looks healthy to me, so I'm going to deny him any medical treatment until someone proves me otherwise. X-ray? Must be fake, since, after all, I can see that he's healthy.