Mundane engagement can be passivity. Behavior has inertia. Humans have widely accepted instincts. You are applying "passivity" too specifically to have much bearing on the truth of behavior. The assumption that a human is going to continue breathing and eating if able is not wooliness of thought. It isn't intellectual malaise to incorporate worldly context into assessments of ethical behavior. It's one of the things that makes relativistic ethics so much fun.
I don't really follow your objection. It's true that our day-to-day actions are a form of concious engagement with the world, is it not? They may not be fully self-concious, (and indeed I would tend to say that there are very real limits on the transparency of the subject to itself), but they
are concious, they are the actions of an engaged subject and not simply the mechanical plodding of a biological object that by happenstance carries within itself a subject, like a pilot sitting inside a partially-autonomous vehicle. That certain actions are mundane or incompletely self-conscious doesn't change this, it simply locates them within a subjective hierarchy of significance.
Eating meat, to take an obvious if imperfect example, is for the majority of people more mundane than vegetarianism, but that does not imply that eating meat is somehow a more "neutral" lifestyle, it means only that it is familiar. It confuses our impression of our engagement with the world with the engagement itself; an assumption that because intellectual adherence to a certain set of norms is passive, the performance of those norms is itself passive. In reality, both vegetarianism and carnivorous are equally definite forms of engagement with the world, and so the ethical distinction we make between the one and the other cannot be found in this area.
What this amounts to, in relation to the question of a "potential life", is that the alleged potential relies on an assumption of habit which has no justification but the very habitualness of the behaviour in question. It may be true that, as you say, this an assumption which most people considering abortion will make, but that doesn't mean that they are (logically) justified in doing so, that they could not take a more critical approach to their situation. People don't need to be prisoners of habit.
I wasn't trying to compare religion and science. I was just saying there's no proof that cells = life, and that certain people give way more value to these cells than to those already living.
I'm not really sure what you mean, here. If "life" is understood as a certain kind of biological process, for which we can establish shared criteria, then it seems a simple thing indeed to establish whether or not a given entity is alive. Only by conceding a definition of "life" as something immaterial, to be identified not through biology but through metaphysical inquiry, would that claim make much sense, and given that you openly reject the possibility of any such inquiry, I really don't know why you'd want to make that concession. Am I missing something?
