I agree with this whole heartedly.
When establishing perameters a safe word is of vital importance. It shows a level of true of servitude and communication that would other wise be lacking.
When you leave an unestablished limit, you are in fact not fully giving in to servitued in that you're playing a guessing game with your D. If you're playing, then it's not a true commitment to them.
Also, I don't feel you're being true to yourself as a submissive by not agreeing to this level of committment, in that you are not truly looking at your own real self and taking responsibility for yourself.
Both parties have responsibilities to each other and to themselves, and those responsibilities are of equal importance.
Again, this is just my own opinion.