It's on par with cogito, ergo sum. I don't know everything, therefore something else exists. I don't feel obliged to cater to people who are unwilling to go along with this.
No obligation on your part was implied. I only suggested tabooing the word "exist" and replacing it with what you mean by it. I bet that you will end up either with an equivalent term, or with something perception-related. So your choice is limited to postulating existence, including the existence of something that isn't your thoughts (the definition of realism), or using it as as a synonym for territory in the map-territory model created by those thoughts. There are fewer assumptions in the latter, and nothing of interest is lost.
http://www.scottaaronson.com/blog/?p=1103
Eliezer's gung-ho attitude about the realism of the Many Worlds Interpretation always rubbed me the wrong way, especially in the podcast between both him and Scott (around 8:43 in http://bloggingheads.tv/videos/2220). I've seen a similar sentiment expressed before about the MWI sequences. And I say that still believing it to be the most seemingly correct of the available interpretations.
I feel Scott's post does an excellent job grounding it as a possibly correct, and in-principle falsifiable interpretation.