Was the argument being made just obviously wrong?
This, primarily. At least obviously wrong by my value system where believing true things is a core value. To the extent that this is also the value system of less wrong as a whole it seems contrary to the core values of the site without acknowledging the conflict explicitly enough.
I didn't think the examples were very good either. I think the argument is wrong even for value systems that place a lower value on truth than mine and the examples aren't enough to persuade me otherwise.
I also found the (presumably) joke about hunting down and killing anyone who disagrees with you jarring and in rather poor taste. I'm generally in favour of tasteless and offensive jokes but this one just didn't work for me.
This, primarily. At least obviously wrong by my value system where believing true things is a core value.
I really don't think that the OP can be called "obviously wrong". For example, your brain is imperfect, so it may be that believing some true things makes it less likely that you will believe other more important true things. Then, even if your core value is to believe true things, you are going to want to be careful about letting the dangerous beliefs into your head.
And the circularity that WrongBot and Vladimir Nesov have pointed out re...
A few examples (in approximately increasing order of controversy):
If you proceed anyway...