Evaluating ETFs is not a trivial process. In many situations ETFs are used to populate specific asset classes, particularly sections of the market that are outside the expertise of ones stock picking abilities.
ETF investors are not inclined to analyze a significant percentage of individual stocks held within the ETF and come up with an overall evaluation. Instead, they will buy an ETF to populate a particular sector or asset class and let it go at that. For example, if emerging markets is an asset class of interest one might choose either iShares MSCI Emerging Markets Index (EEM) or Vanguard MSCI Emerging Markets ETF (VWO) and not pay much attention to the exact holdings within the ETF.