I don't have one now, but I am considering it to have a pure crafter. I am waiting to see if it is something I truly want to do since it is $40 + 15 a month down the road. However, if Jooky keeps up the good work he can have his 30 bucks a month from me.
It may be giving an advantage to those players but they are contributing twice or triple the amount to the games profits and development while not using a proportionate amount of server resources (most aren't playing all their account at the same time).
So in ways they are beneficial to all. Obviously it can be exploited to some extent but I don't think most who have multiple account use it for nefarious reasons.