I don't know... I'd maybe say, that it depends on how you see your tama. For someone who just plays with them 'cause they're nice and fun, but doesn't really hold them as a real sentimental creature, or something that's truly alive, like some people, resetting wouldn't really mean much to them. But if you feel that your tama is alive, even if you know it's really not, (I'm one of these people) resetting your tama, especially when it's just hatched, could be compared to abortion, if you go to extremes. And if the tama is older, it would be like killing your tama, or at least like abandoning a pet pupppy because you don't want it anymore. But as far as killing the tama goes, it would still be 'kinder' to reset the tama if you really don't want it, rather than killing it off and letting it suffer by neglecting it.
but personaly I think that, even though a tama feels very real to me, after I've gotten to 'know it better,' resetting it wouldn't really be that bad. Only if I really loved the tama, I'd feel really bad and sorry that I reseted it, like I'd have killed a dear friend. But that doesn't happen very often. (partially because I hardly ever reset a tama, and partially because I don't always grow so affectionate of one)