cause once players notice any decision of build could be undone, decisions become worthless no matter use it or not.
More nonsense. How is a respec which makes the game more enjoyable a worthless decision? If I do not use respeccing, how does that make a decision about e.g. saving the Grove worthless?
the point of role play is about you believe you are the character what build up by any decision you made. however, in this respec case, I can only believe myself as a Doppelganger
The point of role play is that one can play a role that one wishes. You are not signing a legal contract. Do you feel that multiclassing should be outlawed? Do you think it is logical to just be able to add another, totally different, class to your character because you decide to? What about dipping into several classes for one or two levels just to get certain skills or abilities?
What about mods which fix things that Larian hasn't - are they allowed? I use mods including one to give Lae'zel, Shadowheart and Karlach the stats I would give a fighter, cleric or barbarian. I use mods to make things more in line with 5e. Does any of what I do had any impact on your game and the way you like to role-play?