What First-World problem was being solved by this dress code restriction on the size of logos on shirts at this school? Whatever it is, I find the entire incident to be blazingly stupid and I award the administration no points.
The lawyer problem. If the school has no restrictions on dress, they will, without question, have girls showing up dressed like Kim Kardashian and boys wearing t-shirts that say "Suck My D***, B****!"
When schools try to make rules to prevent this, they are threatened with lawsuits for viewpoint discrimination. In order to maintain decency without saying so, exactly, they have to come up with some kind of arbitrary point, such as "logo size."