Some people seem to be using the "L2P" term very often is balance debates. Imo the term is rude and nonconstructive.
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Imo "L2P" as response is currently overused and should avoided.
Its definately a bad way of putting it, but in balance debates it does have a place. Its pretty easy to copy a working build order, but not everyone can play good enough to make the units fulfill their role.
When used outside of balance discussions however I think it really is inappropriate. You still sometimes see someone asking for help with how to counter something and getting simple "L2P" replies, while hes actually just asking for tips on how to L2P.
As a sidenote, like Inverse mentioned, in tournaments players have to play both sides. Since we do not have mirrormatches, I really wish more people played both sides. Would open up a lot of biased eyes.