The main objection to Lepin is that they steal intellectual property, like so many companies do in China, without any repercussions. Its illegal, but apparently the laws are nearly unenforceable. Lepin does such a good job at replicating parts that I often wonder if they are also stealing molding equipment
Is it okay for someone to make compatible LEGO parts of their own design? Apparently it is quite legal since plenty of companies in the US are doing it.
Also, apparently its quite legal to make parts that are almost exactly identical to LEGO without the actual LEGO trademark on them. (I’ve heard, but cannot verify, that LEGO allowed their patent / copyright / whatever to lapse … or maybe it only lasted 25 years, IDK, I’m not a lawyer and my memory sucks.)
Would there be anything wrong with a third party selling sets that are no longer available?
Is it okay to make parts or sets that are no longer made or never were in production?
One last point, in response to the “frustrated lego builder” article, the people who resell sets don’t really decide how much the sets will sell for, supply and demand / the market does.