The problem is that the tool is both great and terrible. It's basically like a Formula-1 car: ultimate performance, but with huge potential for disaster in the hands of someone who doesn't know what they're doing. It doesn't help that the tool has been growing organically over time, leading to a really confusing UI. Also, it's extremely versatile, but that's both a blessing and a curse, as people can develop totally different and incompatible workflows.

Maybe people need to create some command-line front-ends to git which force users into particular workflows and subsets of the commands, and which clean up the UI, much like how almost no one uses TeX, but instead they use front-ends like LaTeX.

Git is a great data structure with a pretty bad tool to manipulate it. That said, what MBlume said is that one should learn to use the tools one uses (and if you're using Github, you're using git), which is not a defense of git in itself.