I have always been of the opinion that while Christian conservatives decry Islam as evil, they are secretly jealous of it. Afterall, Islam has permeated many governments in the Middle East to a degree which most Christian conservatives could only hope to achieve.
Adult pornography is not generally illegal, true, but unless you actually work in the industry it probably is not appropriate for the office.
Fairly, however, an employee should be instructed as to what is and is not appropriate for work before they can be disciplined for violating it. I remember being presented with an internet use policy when I was hired, as well as sexual harassment training. So it you are told in advance not to do certain things at work, and you freely agree not to do them, you can then be disciplined for doing said actions.
Otherwise one could argue the old "No one told me porn at work was not allowed!" a la George Costanza.
An EULA is a contract, and the first rule of contracts is that they cannot constitute anything illegal. You may sign a contract giving a third party full permission to murder you, but since murder is illegal, a jury will still convict said third party.
Always draw your curves, then plot your reading.
