I'm sorry but I have to say that it's pretty frustrating, as someone who is gay, how people suddenly lament over how undervalued platonic ships are almost exclusively whenever the mere possibility of gay ships are mentioned. It's just a huge downer to come on here after Marco's confirmed to be bi only to see people complain about it.
I take serious issue with the implication that I'm being homophobic. I say platonic relationships are undervalued because that's honestly how I feel, all the time, not just when gays are mentioned. LGBT has nothing to do with the issue. Everywhere I look on the internet, all I see is people talking about how they want to pair up absolutely every imaginable combination of characters (romantically, sexually, and beyond), even if it totally goes against everything the characters in question are and how they feel about each other. I like keeping characters
in character, because violating who and what they are just turns them into a one-dimensional slate for everyone to slather their own personal fantasies onto and kills what makes them unique individuals. It's a whole different beast from just mere alternate interpretations. Tumblr likes to go crazy with the stuff, and that's what bugs me.
I don't have a problem with any of the characters being gay or bi. I just can't see it in Marco. Part of it may be because I'm kinda antisocial and maybe even aromantic. I dunno. However, offhand, I remember plenty of times he's fantasized about/hit on chicks, and none where he's fantasized about/hit on dudes. Like, not even curiosities, really. That would definitely be worth a mention if it happened, given how hard Marco works to cover up all his insecurities, especially if the dude in question happens to be from a different species and planet altogether. Keeping in character, it would create an insane amount of awkwardness and stress for him because he doesn't want to change how others perceive him, just breaking him down under his easygoing exterior. Combine that with everything else going on in his life, and he'd probably end up having a mental breakdown way earlier than he actually did.
This is bigger than Dumbledore, because in this case it actually would have an effect on how he approached his relationships. Dumbledore never sought out a partner. Marco did. If such a significant detail isn't actually in the series, and ultimately doesn't lead to any different conclusions or connect any dots, it might as well not be canon and I have a really hard time accepting it. It'd be like if they said that Rachel's true favorite morph was actually an ostrich she acquired off screen. We don't see her morphing it ever, it's never brought up, it doesn't quite gel with how she acted, and ultimately had no bearing on how she approached things in the series. We know she's pretty cool with bird morphs, but... That's about all there is going for it in the book itself.
All that being said, I found the (very nsfw) fic "Ax the Prostitute" totally hilarious because it was so well in-character up until just before the end.
That seemed to me like a logical angle for the Marco/Ax pairing to work. XD
Anyway, if you want to interpret the character that way, okay. If you want to write fanfic for pairings, that's your prerogative. Just please don't insinuate I'm acting homophobic because I disagree.