I have my reasons for my decision, as does everyone. Although less numerous, I'd like to think mine are better supported than most, but I'm not going to slam any of the non-Z/A supporters. I'm not that kind of person. Live and let live, I always say. Everyone is entitled to an opinion, and those who choose to disagree with me are perfectly welcome to continue doing so.

Reason 1:
It's canon, people. I'm sorry if you don't like what the creators intended, but this is what they set it up to be--let's face it, Zelgadis and Amelia were meant by the creators to be a couple. Now, I'm not saying you HAVE to accept it just because it's canon--this IS fandom, after all. What canon means is that you can't flat out deny that they have feelings for each other. Work around it, yes; ignore it and declare your fic AU, yes; but deny it, no.

Reason 2:
They continue throughout all three seasons to show genuine affection for each other. They casually and habitually touch and laugh, and Zelgadis exhibits a strong, instinctual protective urge towards Amelia. Amelia in turn seems to feel it's up to her to make Zelgadis realize that he's not a monster in her eyes, and she seems nearly as ardent about boosting his fragile self-opinion as she is about The Righteousness of Justice.

Reason 3:
I'm a writer, and being a writer means you study other people intensively and often. Sooner or later, you begin to pick up the clues body language can give you as to the nature of relationships, and become a better writer thereby. While in animation, these cues are not nearly so obvious or pronounced, they still remain. The most blatant one that Zelgadis and Amelia evidence is the fact that they are nearly always seen standing close together. It's unconscious; they don't think about how constantly near to each other they are. This is a cue that I've used in the real world to predict that two people were dating and/or in love, and I'm proud to say I've never been wrong.

Reason 4:
The blush factor. While in real life, this is not necessarily any indicator whatsoever, in anime it means a different thing altogether. Within the rules of anime, when two people are constantly blushing around each other whenever there is a hint of possible romantic contact, this is a clue as to their feelings. It's like the sweatdrop; nobody seems to have trouble interpreting what that means, but yet the blush factor, which shows up about equally as often and which is just as important, gets ignored. Nothing is in there by accident, people. The blush factor means that they're attracted to each other. End of story. Don't believe me? Watch more anime.

Reason 5:
The two of them work well together. While Amelia's justice speeches do make Zel sweatdrop, he tolerates them with a patience I find incredible. I know if I were him, I would have clonked her skull in long ago to shut the annoying noise (I'm not Ami-bashing here, people; you just have to admit, her speeches ARE annoying). Yet he lets it slide time and time again, and listens to what she has to say even when no one else seems willing to. She in turn is frequently found asking, "What do you think, Mr. Zelgadis?", including him in every discussion so that they all have the chance to submit input. Zelgadis, in my opinion, needs Amelia; no one else, especially not Lina, could give him the kind of unquestioning love that she can. While Lina and Zel would be at loggerheads all the time, being both strong-willed and extremely stubborn, Zel and Amelia would be more able to come to a sort of mutual compromise. While I'm somewhat open to the idea of Lina and Zel, I've yet to see them portrayed realistically as a couple--they're too similar to ever be content with each other. Zelgadis and Amelia have that spark of difference that makes them compatible.