I would probably go. I think it's important for the kids to be a part of school activities, even if it's just a learning fair. But, I tend to do a lot of things because my kids will enjoy them, even if they're a giant pain in the butt for me. But, that's my choice.
If I had decided not to do something, for whatever reason, and my husband made me feel guilty...well, he'd be the one taking her to the Learning Fair! LOL!
Men don't realize how much work it is to take kids someplace alone. My husband has taken both my girls out by himself maybe once. He commented on how stressful it was. I was like "Yeah buddy, I do it ALL the time!" He still acts like it's no big deal for me to pop out to the store to pick up one measly little thing. He doesn't get why I ask him to stop on his way home from work to pick up the milk, or the eggs, or whatever else we might need.