I don't know why this isn't legal...or why anyone would want it to be legal. The easy answer to this question as to why it shouldn't work is "why would someone want to mate in their own gene pool?" There would be no advancements in our species and maybe this hurts the government...but i dunno...maybe they just like fucking your mom and don't want you to move in on their territory...

"The belonging you seek is not behind you, it's ahead."
--Maz Kanata