The Raiders were 2-4 in games decided by a TD or less, so it's difficult to say that "Well, they wouldn't have been 4-12 save for a couple of game-killing INTs by Palmer." I mean, they might not have been 4-12, but they probably wouldn't have been 9-7.
According to advanced stats, there's a big spread between his DYAR (334, 18th in the NFL) and his QBR (44.7, 29th), so you'd suspect that he's making some poor errors at pretty significant moments.
But let's keep in mind that Arizona Cardinals fans have been eating metaphorical garbage at quarterback position for three straight seasons. When you're metaphorically eating garbage, Taco Bell starts to look kinda appetizing.