As I posted, secret / anonymous votes are essential as long as there is economic or other inequalities within the voting population. Bribery and enforcement are serious problems. For instance, it is well documented, that you can buy the national "mail votes" of Italiens living in Germany for as little as 40 Euros! One might argue, that for the voting system within a party, secrecy is not as important. However, many, many members of the Pirate Party in Germany broke up with the party, exactly because of this missing feature, when Liquid Democracy was introduced.