That is true when you are speaking about open a situation and let it run forever untill it provides profit, someday it will not comeback and yes, then you are dead, otherwise you are wrong, FOR ME the mental stop loss is a lot better than Fixed Stop-Loss.
Should you open a commerce and dont put a SL, you should be completely concentrated, to be able to close your position when price tells you that you are wrong, you need to be able to control your emotions very well.
Should you dont put a SL and go to dinner in the restaurant, then yes, it's suicide.