MDTech-us_MAN and imrobc
Arduino is OPEN-SOURCE, so this is not illegal.
I think you fail to understand the difference between passing off and open source.
Two members here have reported that their customs have confiscated Arduino clones.
This is for several reasons.
Just because a design is open source it does not mean that anyone reproducing that design has the FCC and other approval that the original board has unless they have submitted it to FCC themselves and have a certificate. Also the design includes trademarks and logos, while these might be in the gerber file it is still a breech of trademark to use them on a product.
The official line is here:-
Remember the money for the official supports other things, like this forum. The considerable server bandwidth and storage it occupies is not free.