Complex sentence: Anti-abortion activists have continued to advance a discredited causal abortion--breast cancer link, and in the United States they have sought legal action to present abortion as a cause of breast cancer when counseling women seeking abortion.
Split into simpler sentences: Anti-abortion activists have continued to advance a discredited causal link between abortion and breast cancer. In the United States, they have sought legal action to present abortion as a cause of breast cancer when counseling women who are seeking abortion.