I have to agree there, a slave in a bdsm relationship makes the decision to give up their freedom in the first place and in reality still has to make some decisions afterwards; the decision to obey can sometimes be a hard one! i wouldn't call myself a slave in the terms we're discussing here but i try to obey my Dom, and when told to do something sometimes obeying requires a conscious effort if i'd rather be doing something else! -obeying is something i choose to do, and even a slave has to choose to obey.
Having said that... when being ordered while we're together i somehow seem to melt into obedience without thinking...
I would love to be his slave, but unfortunately at the moment our lifestyles don't permit it to work. Hopefully one day!

Slaves aren't non-persons because slavery to someone doesn’t remove the feelings or personality of someone, which are the things that make them a person. They may consider them self the property of someone else, but i'd think this is something adding to who they are rather than cancelling out the rest.