I get that it might not be practical for everyone, but I still think you are being selfish to send a child into nursery (NOT school) with a cold sore.
There is more to think about than some random paranoid parent. It's not nice for the staff who have to either risk getting the virus, or stay away from your child. It's not nice for the other children who might end up getting the virus, and who if they have open skin themselves, risk it being more than just a cold sore, and it's not nice for your child who will have staff reluctant to wipe his nose or clean his face.
I'd be getting children to do that themselves if they needed it, so it probably wouldn't be done properly as we are talking about small children here. And I wouldn't be picking them up for cuddles if they needed it. Like I said, I don't get paid enough to risk cold sores. If you are happy with that, then that's your choice.
Cold sores aren't like colds, once a cold is gone its gone. Cold sores come back.
There is a small chance I'm reacting quite so much because a 4yo I was looking after today told me she had been sick twice in the night, and was clearly not feeling well. I don't work in a setting that parents use as childcare while they are at work.