Anything less than 100% certainty is an unacceptable risk that innocent life will be taken.
There will never be 100% certainty that something won’t happen. You cannot prove a negative. I do think that there is more work that needs to be done, but there isn’t ever going 100% certainty that something can’t happen.
I am hopeful that there will be a point where Plan B can be used in cases of rape and within Catholic teaching. We aren’t there yet. Rape victims are important too, and the trauma of pregnancy in addition to the rape can be horrible for some. Prevention of pregnancy in such a case would be a wonderful thing.