Seashells in Phuket - 2 buy or not 2 buy?

A question that I get a lot is that tourists are not allowed to take shells from the beach  - including coral that is broken – Why?

But there are are shells for sale all over Phuket - the above photograph 
was from Rawai - 7/6/10.

I can only say that the shells that are found scattered on the beaches in Phuket are the homes of a number of marine creatures and is the sand for tomorrow’s children.

It is thus illegal to sell seashells from the waters of Thailand – but I hear visitors cry that there are shells all over Phuket for sale!!!!!! 

These shells (so I read - but how do I know?) are mostly from Indonesia – so it does not matter if it the sand for children not in Thailand or the homes for marine life not living in Thailand?