The vast majority of people here are posting sane, sensible things to defend without considering the wide range of implausible conditions and situations that my brain immediately leapt to, like if aliens used to mind-ray that made all people with at least 1/4 Welsh descent incredibly callous, strong and prone to fits of murderous insanity, therefore making it not only acceptable but necessary for personal survival to discriminate against those with Welsh descent.
I am disappointed in you all.
Anyway, even taking the above statement into consideration, the one thing I would most certainly defend is the concept and act of scepticism (Or skepticism).
All beliefs should be challenged every now and again, just to make sure that they're still the right ones. You wouldn't just virus scan your computer once, so you should, on occasion, scan your brain for bullshit that may have gotten in there. Question your beliefs constantly, make sure they're still good. Failure to do so leads to stagnation, and that way leads to discrimination, genocide and gone-off milk.
And for any burgeoning White Knights[sup]TM[/sup] out there, I'm Welsh myself, so it doesn't count as racism, ha!