Her sentiment was echoed by Josh McClure, the executive director of a California pregnancy clinic.
"No American should be forced to preach a message or speak a message that they don't agree with. That's the basis of why we're here," said McClure.
O'Connor also said that while the justices posed "challenging" questions, she believed that at least eight would rule in favor of NIFLA.
"But 9-0 is what we're praying for."
Pro-life advocates braved the freezing temperatures and rain to show their support for pregnancy centers.
Kelly Picardi, a non-denominational Christian, told CNA that she and her husband are in the process of adopting a child conceived in rape, due to be born next month.
"The conception of our daughter's life came about through a difficult and unfortunate situation, but the decision of the birth mom not only choose life but to choose adoption is the most respectable thing I can think of," Picardi says.
"That kind of decision is our inspiration, and an example to [my family] of what love looks like. Even though she's had a really hard life, [the birth mother] is still making the kind of decision that will benefit someone else. That example of love is what we'll live by every day."
Picardi says she hopes that her family's decision to adopt can serve as an example for others, ultimately helping to normalize the practice of adoption in society. "As hard as the adoption journey is, it's really been affirmed by the people in our community," she said. "Good can always come from broken situations."
Rosemary Geraghty, a new media coordinator for Rehumanize International, said her beliefs as a self-identified feminist put her at odds with the pro-choice side of the argument.
"It's hard for me to understand why someone who would call themselves pro-choice would be against the groups that give women more options than just abortion," she told CNA. "To attack these pregnancy centers that are giving direct aid and resources to low-income women and pregnant people...it's just anti-'pro-life people.' It's viewpoint discrimination."
(Story continues below)
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Jeanne Mancini, president of March for Life, stressed the important work that pregnancy care centers offer to serve women in need.
"The bottom line is that abortion hurts women; it doesn't do a service for women, and these centers can provide women what they need in a very stressful moment," she said. "Things like diapers, but also more complex things like housing, education...these things are critically important."
Jonah McKeown contributed to this report.