It's a bit baffling how "some economists" weren't fully cognisant of what would happen when the minimum wage was raised. I mean it's not as though it's the first time it has happened, the effects should be well known by now.
The problem is that it's not clear what happens when the minimum wage increases. It's also not clear whether something different happens when a city or state does it versus a national change.
Case in point: thirteen states increase the minimum wage and employment increases faster (on average) in those states than in those that do not increase the minimum wage. The presumption in the post is that the causality is that increasing the minimum wage causes employment increases. What if the causality goes the other way? Increasing employment could make states more willing to raise the minimum wage. Correlation does not indicate causality, so economists can't differentiate between the two explanations.
There's actually been quite a bit of study of the effects of raising the minimum wage. The problem is that it's impossible to produce a real double blind study. Without that, there will always be reasonable doubt. In one study, they won't be able to eliminate the possibility that employment would have gone up faster without the change. In another study, they won't be able to tell if people are moving from the comparison area to the change area for the higher wage jobs. In another study, perhaps employment increases occur because kids drop out of school to take jobs.
Economics isn't anywhere near as mature a science as physics or chemistry. It doesn't lend itself to repeatable experiments. Without objective data, subjective opinions take a far greater role.