I too browse /r/AskReddit. There are a lot better ones in that thread than this, FWIW. Any [aspiring] film buffs out there should take a few minutes to read through this thread.
Also, for the record: Leonidas explicitly tells Dilios to dramatize the events before he sends him back to Sparta, to tell of the warriors' sacrifice and inspire Greece to unite against Persia. This isn't some secret layer to the film or anything.
I think it's a bad movie. The old one (The 300 Spartans) was much better IMO.
Bullshit, it's completely relevant. This isn't a documentary meant to educate, it's a movie meant to entertain. It'd be one thing if it was inaccurate due to poor research or lazy writing, but they literally explain the reasoning for the inaccuracy (along with the visual style of the film, the excessive violence, etc.) in the movie itself -- and also in the graphic novel. That's purely a stylistic choice, and IMO it works quite well.
How do you feel about Braveheart? The Searchers? Inglourious Basterds?
I'm not saying I think 300 is a good movie, for the record. But to say that it inherently fails by virtue of the historical inaccuracies is a copout that undermines the entire purpose of the film. So again, I say, bullshit.
Your criteria are flawed. These are not documentaries, nor do they claim to be historically accurate. To judge them solely on the merit of their historical accuracy is utterly nonsensical.
I'm not saying you should completely disregard the historical inaccuracies -- it's good to be aware of such things, and there's nothing wrong with giving them a bit of weight with regard to your overall assessment of the film. But it's simply absurd to base your entire opinion of a film's quality on its historical accuracy. Especially in cases where historical accuracy was a conscious design choice that actually supports the narrative.
To make 300 100% historically accurate would have conflicted with the entire purpose of the film. In truth, this would have made it a worse movie, due to the narrative inconsistencies that it would have created.