Sure, until people realize that politics have the capacity to impact their lives negatively, and then all of a sudden the rationality for discussing it is quite clear.

> One way of excusing yourself from such a conversation in a (hopefully) unoffensive way would be to make an honest statement like, "Gosh, my brain is so overworked right now that I can't even begin to delve into the nuance of that subject, but I hear where you're coming from."

I wouldn't characterize this as a polite excuse so much as an honest admittance—you clearly respect the other person enough to indicate an acknowledgement of the meaning of what they're saying and an incapacity to respond. That is, unless you're lying, which is clearly disrespectful. In that case a "I don't agree but I feel like it's unprofessional to engage in these conversations" would suffice.