Many years ago a little document called the Declaration of Independence was written.

We hold these truths to be self evident, that all men are created equal, that they are endowed by their creator with certain unalienable rights, that among these are Life, Liberty and the pursuit of happiness.

I think democrats look at this declaration like this...

Who's to say,  there is a creator.  Who's to say,  when a life begins.  Who's to say what Liberty really is.  And pursuit.. you mean we have to persue!  

Who's to say?