Richard Cohen disses the Republican field: "Ignorance has become more than bliss. It’s now an attribute, an entire platform: 'Vote for me, I know nothing and hate the same things you do.'"
The best way to think about this is probably as a principal-agent problem. These arise all the time in economic life. You want to invest in shares of companies that you don't manage. A difficult question then arises of how do you structure the firm such that the people who do manage the company are advancing your interests rather than simply using their control over the firm to do what they want. The main device we seem to have hit upon as a society is stock options. It's not obvious what the analog of that would be in politics. Republican Party primary voters need to pick a standard-bearer who can't be given "shares" in the overall success of the conservative movement. How do you find a reliable proxy under those circumstances? Hating the same things seems like an excellent heuristic. Actively selecting for ignorance is more problematic, but it too makes some sense. Someone who gives the impression of not being very interested in the details of public policy seems like someone likely to just be guided by his sentiments of hatred and team spirit. A deep thinker might decide that his co-partisans are wrong on the merits even if he hates the opposition. An ignorant agent isn't going to be the optimal choice, but given the need to make a choice under conditions of uncertainty it seems like a reasonable satisficing approach.