I'm sorry but your have your facts wrong.
Seeds cannot be accurately classified as an addictive controlled substance. There is too little THC or CBD (controlled substance) in a seed for it to be classified as addictive. There may be trace amounts of morphine in my poppy seed rolls but my baker doesn't promote substance abuse.
A seed is the starting point for all life on earth. You started life as a seed in your fathers testicles (the word sperm is derived from the Greek word σπέρμα or sperma meaning "seed").
Cannabis seeds are legal to possess, collect, buy, sell, trade etc. in many countries of the world. It is LEGAL to buy seeds in Spain, as it is in Ireland, England, Scotland, the Netherlands, Belgium, Switzerland, Austria, Poland, Russia, Italy, Canada, Japan and so on. The possesion or sale of hemp seeds in these countries is not a crime (1961 Vienna Convention). Border control cannot confiscate something which is classified legal in its home country.
OP is not promoting substance abuse and it would be foolish to suggest so. OP is not condoning the use of cannabis. Germination of cannabis seeds is a completely different matter and OP would in no way encourage anyone to germinate seeds in a country in which it is unlawful to do so. It is unhelpful at best when people who haven't done their research make sweeping generalisations based on their own predjudices.
OP please reinstate your post. Providing you are shipping only to countries where possesion of cannabis seeds is legal then there is no problem here. One could argue that the preservation of genetic specimens for future generations is doing some good for this crazy world we inhabit. Some forward thinking governments are doing all they can to encourage this...
http://en.wikipedia.org/wiki/Svalbard_Global_Seed_VaultCurrently 13,500 individual cannabis seeds stored...
http://www.nordgen.org/sgsv/index.php?app=data_unit&unit=sgsv_by_species&unit_id=1666599