And more pragmatically - the entities and relations evoked by a religious worldview are, by and large, denied or strongly contested. The fact of human suffering caused by unsubstantiated doctrines, is not.
To put it a little more bluntly - of course religious worldviews shouldn't be forcefully imposed upon all. And certain ethical principles will of course have to be imposed on all. For this is what we agreed to in our hypothetical social contract. Right? Give away some of our freedom in order for the state to guarantee as as much freedom to all as possible in a civil social setting. Now hashing out the details of how these freedoms should be defended from those of others is what ethics is all about. This is what everybody wants. A heaven-on-earth is what a select group of people wants. And the latter is one of the considerations that the former should be defended from. What makes a theocracy work is that ethics and religion are in such a system inseparable. In modern democracy they are separated, and ethics trivially takes the primacy.
To the second - well, yes, technically. Despite the fear of coming off as some devil-worshipping callous maniac, I do accept that a reasonable case can also be made for infanticide, for instance. I am not myself in favor of infanticide, but at this point this is just a gut reaction and not a view held for any serious philosophical considerations. Some thoughts on it revolve around the social connotations of this practice and the possible emotional and social effects of such a practice. However, this is quite irrelevant, for all I am saying is that the project of defining life (and indeed, very strictly defining it) is a red herring in the matter of abortion. I have my doubts that a definition satisfying all even can ever be found. I'm fine with leaving the line to whatever those involved (or not) are more-or-less comfortable with, as long as the woman has ample time to make up her mind and the doctor doesn't feel like a butcher. Or why not, stress the consciousness angle, and even be safe about it by tying it to certain developmental stages of the brain, as we admittedly know very little of consciousness.
Finding a self-evident guiding principle that would solve the whole issue, seems a conceptual impossibility to me. What, however, is relevant, is the fact of the matter that people are currently being shamed for their decisions, or even forbidden to make some serious decisions about their own bodies because of some incredibly arbitrary, and often self-serving, criteria.