I think this was a good decision. It is realistic and will let people who want to as RP married or family have the same last name. Or just to have aconnection to a friend. There was no reason to let it be uniqe in the first place.
Look at this as a hand to all the complaints about having to change names after server merges and as a first step to letting you link legacies with someone else.
I expect that after we are all allowed to pick new legacies they will start looking at first names too.
To all the ones who clam that pepole can impersonate you and get you banned just by taking you Legacy name. Do you really think that Bioware ever uses Legacy name to decide a ban? That's just idiotic. They have unique identifiers for your characterts and your account, thats how the underlaying database works. All databases. They will know if someone else is impersonating you.