I have read that Nicholas and Alexandra truly did not feel like going to that ball, but they felt pressured to attend by Nicholas's uncles, who convinced him to go for diplomatic reasons, as the ball had already been arranged and for them not to show up would have been seen as a slight to the French Ambassador. Of course, the Russian people saw this move as a slight to themselves, and perceived their sovereigns as being insensitive people who were dancing the night away at a fabulous ball while their subjects grieved over this terrible disaster. But they seemed to forget that the Imperial couple spent that day visiting the injured in hospitals and were said to have danced at the ball with red eyes due to their sorrow; they were deeply shocked and moved by this disaster.
Personally, I think it would have been better if they had not have gone, thus showing their support for their people at a difficult time and mourning with them. I would think that the French Ambassador would have understood what a delicate situation this was and he should not have felt personally insulted. But even if he did, then it still may have been worth offending him and gaining the love and support of the Russian people, who were the ones whose opinion really mattered in the end. At the time, I suppose it seemed a better idea to appease the diplomats, but this whole incident did not look good in the eyes of the common people and it was just one more thing for them to resent the Tsar for. People already saw so many bad omens early on in their reign, from Alexandra arriving behind her father-in-law's coffin to the Khodynka disaster and then this whole affair with the ball. They just started adding up strikes against them, and I think if they would not have gone to this ball, it would have been just one less strike.
Yet I can't blame the Imperial couple for going, as they were brand new sovereigns without much experience in diplomatic matters and relied on the advice of their relatives, which in this case just happened to probably have been bad advice. They felt pressured both ways and just happened to decide in favor of diplomacy rather than sensitivity, and I suppose they were haunted by this decision when all was said and done. But as they say, "hindsight is 20/20."