(1) I don't care whether or not we are able to choose our own behavior. I experience the world as it stands, within which we are at least given the illusion of choice. That is, honestly, good enough for me. If the issue is that criminals and people we sentence to death/imprisonment/etc. couldn't make any other choices... then the argument also stands that our punishing them in any given way is also due to our inability to make other choices on those matters. It's moot. The "excuse" works both ways, and when that is true an argument on the topic is a zero sum game.
(2) As I already stated, there doesn't have to be "something wrong" with hurting an animal to understand its suffering in your own terms. There don't even have to be "ethical precepts". Your understanding, and a desire not to act like a fool by thinking yourself beyond reproach or thinking "this will never happen to me" while you execute something of a particular nastiness (as you, yourself would perceive it if it were happening to you, obviously) on another being is all that is necessary to "keep you in line." And if that doesn't work, then you likely aren't thinking about things before you act. If those tendencies and understanding lead me to seem like I "conform [my] behavior to certain ethical precepts" - oh well. It doesn't mean I care any more or less that you think such ethical precepts exist independently of man himself.
I desire my freedom, likely as a biological/evolutionary imperative. I also desire to be smart about the things I do and the choices I make. Is the truer issue here that you want to know where THAT drive comes from? It's not from any "objective" reality of "right" and "wrong", I can tell you that much. At a certain point it is simply what calls to me, but I am sure it is still rooted in some need to be the master of some particular domain. To be the "alpha" in some aspect of existence. Taking out all other external aspects that are not under my control, I am left with myself... and so I go about the business of figuring out what the best methods of control are, what the best ends and means are. Within that search I find things that make sense, things that don't make as much sense. Things I desire to emulate, and things I find deplorable.