When someone says that piracy or taxation are theft, they are not necessarily appealing to intuitions about theft. They may literally hold and mean to state that they share with carjacking whatever makes carjacking theft, WITHOUT sharing other properties of carjacking... in effect, this is a thesis statement rather than a knock-down argument.

Of course, it is also possible that it is not even an honest appeal to intuition, rather just an emotional tarring which will never be substantiated. This is usually what is irritating about hearing those arguments.