Factual error: In season two the show makes Dalton look like it's in a suburb of Lima. Dalton Academy is suppose to be located in Westerville, OH, which is two hours southeast of Lima. Kurt & Blaine would not be able to go to the "Lima Bean" coffee shop every day if this was the case.
Factual error: After he gets fired from his teaching job, Mr. Ryerson makes a living reselling the medical marijuana he receives for depression. At the time the episode was made, Ohio was not one of the 16 states (and District of Columbia) that had medical marijuana laws, and NONE of the states allowed it for treatment of depression.
Factual error: They sing Katy Perry's "Roar" before the song was even released. This episode is set in Spring 2013 and the song was released in August.
Factual error: The wedding is at a Christian church performed by a Christian minister, but at a Christian wedding the groom stands on the Minister's left side and the bride on his right. The way Will waits for Emma is the way that the bridal party stands at a Jewish wedding.
Answer: The show is purposefully stylized and over the top. It is not designed to be an accurate, realistic representation of American high school. The idea that the glee club is so unpopular other students can literally throw garbage at them with impunity is an over-exaggeration of how glee club is considered "un-cool" compared to things like football. However, there is a second way of looking at it. The audience is simply never shown anyone getting into any trouble for throwing slushies. Just because we don't see it doesn't mean it never happened.
BaconIsMyBFF