Wow!!! I can certainly understand your fears. When you have a baby, you think of all the bad things that are out there and as a good parent you want to protect your baby from it all.
I'm really not sure if your baby could contract a herpes virus from kissing on the forehead? That is a really great question. I wouldn't let anyone with a cold sore or other lesion around or on their mouth kiss my baby, you would think someone with cold sores, etc wouldn't want to, but some people just don't have any common sense.
If people kissing your baby bothers you that much, don't let them. This is your baby, and people need to respect your decisions. You are the mommy!!!