If a you believe that a fetus is not a living human, then it's a reasonable position to see terminating a pregnancy on the same terms as removing a benign tumor, or wisdom teeth, it's an unwanted growth in the body.
If, however, your belief (which need not be tied to any religious leaning) is that a fetus is a living human, then the only reasonable conclusion is that it has all the rights assumed to exist for all other humans, most fundamentally the right to life. Western civilization has long agreed to such fundamental rights, separate from any religion.
Believing that a life starts at conception but also stating that you're not going to impose that belief on others and tacitly allow them to kill living humans (per the belief held) effectively forces there to be a class of humans for which it is acceptable for others to believe they have to right to kill members of that class at will.
Someone holding such a position is a truly vile person, a spineless, mealy-mouthed, failure of a human; one so craven that they lack the courage to stand up and speak out when they believe that thousands of helpless people are being murdered.
Even if I don't agree with the pro-life position I can at least respect that from their point of view they sincerely believe they are working to stop the deaths of people unable to speak for themselves. That is at least a rational and humane position.