There's not a lot in this section that I find actually objectionable, but it is a good example of an interesting phenomenon prevalent in the early church that's absent in the modern church: personalized scoldings from God.
You could make the argument that the minutiae of callings and missionary assignments in this chapter still come from God in a similar fashion today, albeit through more recently established pipelines and without being canonized as scripture. But chewing out David Whitmer by name—as well as plenty of other church members throughout the Doctrine and Covenants—is not the kind of thing that happens in Mormonism anymore. Discipline is usually more private in 21st-century LDS culture, which is better. But it also comes from a man who's several levels of authority removed from being able to hear God's voice, which is worse. God used to have the guts to set people straight by name in his own words, but now he hides behind a bishop and a stake president.
One last comment I want to make on the closing verse:
And your whole labor shall be in Zion, with all your soul, from henceforth; yea, you shall ever open your mouth in my cause, not fearing what man can do, for I am with you. Amen.
Advising people that there's no need to fear what people do is a bold statement for God to make, especially in the same year he oversaw publication of a book of scripture featuring the gruesome deaths of other people whom God was ostensibly with—like Abinadi and the righteous Ammonihahites. And, of course, the mouthpiece God is using to make this statement will be tarred and feathered, driven from Illinois, driven from Missouri, thrown in jail for months, and eventually murdered.
So you'll have to excuse me if the advice not to fear what men can do because God's totally got your back rings a bit hollow for me.