I see your point about Shichika, but I also think he is not as heartless (in the true sense of the word, because objects don't have hearts) as he seems. I'm not sure if I will like him any less if he really is indeed just a sword, but I am still hoping that his comment about a sword choosing a master and having a will of its own implies that he is not a mere tool either. It may be like that now, but maybe he will change throughout the series. It is always good to have well-rounded characters that change appropriately as the story goes on.

I think that the reason Shichika (possibly) does not care at all at present is because of his lack of experience and human contact. Maybe his travels with Togame can change that.