if some state declare it clearly that buy and selling of bitcoin is illegal then certainly it must be illegal for the poople of those countries. and those countries who have no statement about bitcoin or those who has consider the buying and selling of bitcoin legal then it is not illegal. then it is legal there.
if selling of bitcoin is illegal then buying of bitcoin will also be illegal. then you buy it. i think selling of bitcoin in some countries will be illegal but just like the drugs but in some countries where they have legalize it there it will be legal to sell or buy it.