The classic answer is that your confidence intervals are liable to occasionally tell you that mass is a negative number, when a large error occurs. Is this interval allowing only negative masses, 90% likely to be correct? No, even if you used an experimental method that a priori was 90% likely to yield an interval covering the correct answer. In other words, using the confidence interval as the posterior probability and plugging it into the expected-utility decision function doesn't make sense. Frequentists think that ignoring this problem means it goes away.