Here's what I think: if the lead in your lipstick were your only exposure to lead then sure, no big deal. But lipstick is just one of countless sources of lead (not to mention other toxins) that we come in contact with every day. It just makes sense to minimize your exposure whenever you can, don't you think? It's especially important for people like me with a chronic illness.
Not to mention -- lipstick goes on your mouth! Think about how much lipstick you inadvertently ingest every day.