Toi: The Avnei Nezer brings down that even if you say that Biah B’miktzas is Assur and even if the thickness of the wall counts as Biah then there is still no reason to say it unless you get to the halfway point of the wall. Also, this is only an issue if someone is a Zav/Metzora/Ba’al Keri. A T’mei Meis is allowed on Har Habayis.
Mak: Anyone who says not to get close to the Kotel is using the false assumption that the Kotel was a wall of the Beis Hamikdash.