I don't know how many of you watch Steven Universe, but one episode had a fantastic moral about how love at first sight doesn't exist and how real love takes time, work, and communication, and that you at least have to know the other person. Also, just because someone has a crush on you, you're not obligated to return their feelings. As you all know, these are all problems with Flashlight: they don't know each other, they barely communicated at all, and that's not even getting into the whole teenage human/adult pony thing. Basically, love at first sight is just a cheap trick to force a pairing and the fact that they did it to Twilight is just an insult to her character, as well as Flash for being made solely to be a satellite love interest.

4835789 I have to agree and there is so much else wrong with the ship it's not even funny. For one thing the Flash that pony Twilight had a mild crush on (and I even think mild is too strong) lives in the human world. Even if they could work a long distance (not to mention cross dimensional) relationship via communication, what happens when there is no intimacy? The relationship would fail. I mean seriously, would either of them really have time to work on the other aspects that make a lasting relationship, intimacy being one. What about if they took it to the next level and wanted to get married? Would Human Flash abandon his friends, family, dreams just to go to Equestria? Would Twilight do the same to go to the human world? Let's not forget that to do so she would also have to abandon her responsibilities as a princess. Some would argue that to circumvent the barriers one could have Twilight fall for pony Flash, yet in 'Equestria Girls' (only mentioning EQG because their interaction in the following two movies was practically nil) it's human Flash she has a thing for.
As to your other points... you hit the nail right on the head. Forcing a love interest on Twilight was a grave insult to her character and as much as I really don't like Flash's character, it was insulting to him too. Every time I see the pairing I say 'Come-on man!'

4836298
Well, I highly doubt Hasbro will ever address any of those problems. More fics I'd like to see are less 'Flash is murdered' and more 'Twilight goes "What was I thinking"' or 'The relationship fails almost immediately'. I did have one particular idea but no one seemed to like it...

4837426 I personally haven't read any 'kill Flash' fics. I mean the guy may be a tool (read: plot device) but he doesn't deserve to die. I'm working on a fic where he was a past flame but that's about it. But yeah they probably won't fix any of the issues.

Love at first sight is a trope that many fans of romance enjoy for some reason or another I've never fully understood, but my guess is that they feel it makes it more romantic because it's like "you just know they are meant for you," though in reality love at first sight is a lazy writing tool to allow individuals to make characters fall in love without having to justify or build upon how that love makes sense.

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4839651
Twilight: Look, Flash...just forget it. It'll never work between us.
Flash: But Twilight, I love you!
Twilight: No, you don't! You don't know anything about me! And I don't know anything about you either. Even if we did, it wouldn't help. We're from two completely different worlds. I have responsibilities. You literally have no idea who or what I am. Maybe I'm partly to blame for contributing but I know this much about love: it needs to be more than just a crush.

Human RD: Dude, she's a talking pony. Did that seriously not weird you out at all?

Flash: So...
Human Twilight: Oh no. No way am I going to be a rebound girl. Plus, how do I know you won't just be using me as a surrogate for her? And that's not even getting into the fact that we know nothing about each other and that I am in no way obligated to indulge your crush.

4850656 that could work. You should write it.

4850724
Hmm, perhaps. How would it start, though? Rarity and others pestering Twilight about pony Flash and she realizes she needs to deal with human Flash?

4851987 Maybe not that so much as them pestering her about human flash; then she gets tired of it and has an epiphany that it would never work out.

4850656
That'd be the reality of it. Love at first sight is just not real; what's really happening is you're seeing someone pretty and saying "I love that face" - you don't care about their personality until you're forced to, and with a character like Flash who lacks a personality it's like an eternal stalemate which has nowhere to go. Even pairing Twilight with a villain or otherwise unsympathetic character would yield better results, if only for the drama and the element of the forbidden.