The thing is, he's allowed to have opinions about abortions, in general. But his opinion on abortions in general is almost irrelevant - because he's not entitled to her private information.
It's also worth noting that he's not the baby's father and in no way directly involved with the pregnancy. And that even the father of this pregnancy isn't legally entitled to know if she terminates. Every person has the expectation of privacy around their medical information.
I think we're getting into irrelevant things, here. The topic at hand was whether OP should tell her husband. And the consensus is that it's not her secret to tell.
As a grown adult, his daugher is allowed to have privacy over her private medical information and to expect that if she asks someone close to her to keep something in confidence, that they will do so unless it's an emergency that warrants revealing it. Nobody in her life is entitled to know about her abortion unless she tells them. Not even a parent.
OP is a good mum, she's supportive and entirely reasonable to discuss this here because it's weighing on her to keep a secret. I feel bad that the thread has gone on many tangents rather than answering her question.
And it sounds like the daughter may tell her dad at some point, and that he will probably eventually be supportive. But right now she needs privacy and to know that her mother has her back.