Would have been nice to open with that. Instead of the asshole comment "don't be that guy" look at it from my perspective. No one here stated why I couldnt/shouldnt.

Except where you were told this: "Winlink is slow.. Really really fucking slow. And take a really slow spotty HF connection and pump 67k of data through it is just hosing it for everyone."

Then you came back all defensive with this:

How big of a msg is acceptable? 10k, 20k? Who determines the size? If it isn't prohibited why do you believe you know what is best? Isn't that a bit arrogant?

You were fine asking how big of a message is acceptable. Then you went off the rails. You're the one who came here looking for advice. But then you want to follow it up with "Who determines the size?" and "Isn't that a bit arrogant?" I can empathize with wanting more information than you were given, but when you're given an explanation, and you respond as defensively as you did, you're not creating an environment where someone is going to want to take the time out of their day to explain why it would be inconsiderate to tie up a frequency and a Winlink node for a half hour or more.

The only reason I was given was 'because we have been here longer and we said so.

That's not true. As I mentioned above, you were told that the transfer would be really slow, and you'd be "hosing it for everyone." You might not LIKE that reason, but you WERE given one. But even if it was true that the only reason you were given was "we have been here longer and we said so," try to keep in mind that you came here looking for advice? Why? Because presumably we have been here longer and presumably we know better than you do. You're basically getting pissy because you're being told "that's a bad idea" instead of "here's how to accomplish your bad idea".

Furthermore, the reality is that amateur radio is very loosely regulated. The reason that is the case is because it's self regulated. Do you know what self-regulation means? It basically means people who have been around longer and know better telling others what are good and bad ways to do things. Learning from others who know more is a fundamental part of the amateur radio community. If you're going to get all pissy every time someone tells you that's not a good idea, and gives you a less verbose reason than you wanted, then quite honestly, this isn't the hobby for you, and you should probably avoid the internet too.

It looks like you wouldn't have an issue if I kept my transmissions under 10 min I'd be ok in your mind.

10 minutes would be a legal requirement, since legally, you must identify every 10 minutes, but a 10 minute back and forth with a Winlink node seems like a lot. If you were pulling that once a day, that would seem fairly reasonable though. I have an issue with how you're approaching this though, which I'll get to in a minute.

If anyone had bothered to understand what a GRIB file was you would see that I can actually do that.

What the file is doesn't matter. They were going off what you said the file size was. If you can get a GRIB file that is smaller, great. In your post though, you said 50kB. Don't get upset when people use numbers YOU provided.

To come back to the thing about your approach that bothers me...you come across as caring only about what the law says, seemingly ignorant of the fact that this is a hobby that is built on self-regulation, rules of thumb, and gentlemen's agreements. Your mindset comes across as "if it's not illegal then fuck you, I'll do what I want" and I think you can see why that doesn't elicit a friendly response from people.