Question : Why is it so bad to run a DC over a public namespace?

Ok, I'm sure i'm opening up a can of work with this one, But Why is it taboo to have a domain controller over a public namespace?  I have never heard a definitive answer. I have heard this is wrong wrong wrong, but didn't that used to be common practice?

Answer : Why is it so bad to run a DC over a public namespace?

My AD domain name corresponds to our public domain name.  It can be a bit of a pain (e.g. opening Internet Explorer and going to http://domain.com/ gets you our Domain Controller, not our website).

Can't say I really have any issues other than that, and needing to manually maintain some DNS records.