Space travel has not been very safe. Using rough data from a variety of imprecise sources, it seems that there have been about 700 human trips into space (or toward space if you count disasters during the ascent phase) and about 30 fatalities from all countries combined, 14 of which were U.S. space shuttle accidents. So, the fatality rate per person-trip is something like 4%. It should be somewhat similar per flight, even with the high number of fatalities for those 2 shuttle disasters because of the fact that there are usually more than on crew per flight, often 3 or 4.
So, if you were already embarking on a mission that has a chance of about 1 in 25 of killing you, and you learned that several things were wrong with the vehicle, which was made by a company that was just convicted of negligence in designing and manufacturing aircraft, I think it would be only a sign of intelligence if you demanded that the problems be fixed before you risk you life to test the thing.
That said, there has been no indication that either of the astronauts were unwilling to fly the Boeing capsule back to Earth. The hesitancy seemed to be getting expressed by the engineers on the ground who were concerned for their safety.