You probably mean that Nami was ignorant to think that the beast pirates didn´t attack Tami right?
In case I would not call it bad writing but more a logic fail of Nami and Usopp, they put that child in danger in the moment when they use her ability to get the smile on their side. In that moment they risk the life of a children and are mad that the enemy try to resolve the problems, since Tama was a big danger for the entire beast pirates.
In my opinion Nami and Usopp can be even happy that Tama "just" get slapped, with her position and power, who is sooo important, in our real life she would be killed for sure in a war, sadly that is the case in a bloody war, they not look if you are a women,children, as long as you beeing a big danger for the country(in this case Onigashima/wano) they kill you. In terms of war aspect, Tama done crazy shit against the beast pirates and the slap is nothing for what Tama get if she beast pirates caught that poor girl. We speak about a pirate crew who killing childrens/familys. They literally try to kill Momo, if the Scabbards didn´t save him he would be dead now lol. King still try to kill a 8year children. Nami and Usopp fault are to allow Tama to play a big part in this war, she will be a threat for every beast pirate.
Everything is funny until a 8year old children get killed in a war, very ignorant of Nami and Usopp to use that poor children who is now the target of the beast pirates.
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Not working, Tama was knocked out after Kaido almost kill her, yet Speed was still under her control, don´t ask me though why this is possible