Writing an essay about a topic like abortion is quite difficult, as many people have fairly strong opinions about the subject and are often disagreeing not just about conclusions but about fundamental premises.

Your first step is thinking about your audience. In order to write a convincing essay, you must use the sorts of evidence that your audience would find convincing. For example, a Christian writing to atheists could not cite the Bible, as atheists (or Hindus or Buddhists) would not find the Bible convincing.

Instead, you might look for common ground in issues such as maternal health or sympathy for families who cannot bear children looking for children to adopt.