Like all things, moderation seems the appropriate rule. But doses of parental spit might be a good thing for your baby.
Sucking Your Child’s Pacifier Clean May Have Benefits
Children whose parents had no problems sucking their pacifiers to clean them had fewer allergies, lower rates of eczema and fewer signs of asthma than those whose parents typically rinsed or boiled th…

I don't know how prevalent it is anymore, but in some places a parent chewing a weaning babies food and spitting it into their mouth was common practice.
Well in the days before access to Gerber's Baby Food, I can imagine that as a more convenient alternative to mashing something up with a fork or spoon.
On the other hand, there are a lot of "common practices" in child-rearing whose wisdom is debated these days. 🙂
Sure. Like vaccination. Independence. Reading. Exercise. Manners. Respect…