There's a massive difference. Going on a plane is optional/voluntary, and those with babies or who are vulnerable have the choice not to go on a plane. The OP is talking about a completely different scenario where a covid positive person, in fact a health care professional, is coming into their home, potentially spreading the virus, and the mother won't have a choice! Can't you see the difference. I can't see any double standards at all.
My OH is ECV due to incurable cancer. We have made the "choice" not to go abroad again as we've decided airports, planes, etc are simply not safe enough. But he has NO choice to go to hospital for his infusions, consultations, blood tests, etc.
Hence, personally, we don't give a toss who goes on planes, whether they're covid positive or not, because we're not putting ourselves in that position of risk. However, we DO care about the healthcare professionals that OH has no choice but to come into close contact with due to his treatments, etc.
Surely you can see the difference?