I didn't mean faeces as condom replacement, this is what some Egyptian women used. However, it was also thought of as an aphrodisiac.

As for the STI's, yeah thats one pitfall, but I can't help but think one would be smart to carefully select who they lay (with).

You'd be surprised. Some people don't even know they have a disease because it can lay dormant for a long time. HIV can take up to 8-10 years to develop into AIDS. And then there's diseases like Herpes which come in waves but even if someone doesn't have open sores on their genitalia doesn't mean that they can't give it to their partner.