John Calhoun writes in Slavery a Positive Good that slavery is not that bad because he defends it that the country as a whole kind of needs it. He try to make an argument that try to stop it is bad and compares it as an infection on the country. “As widely as this incendiary spirit has spread, it has not yet infected this body, or the great mass of the intelligent and business portion of the North; but unless it be speedily stopped, it will spread and work upwards till it brings the two great sections of the Union into deadly conflict.” He gives examples of how the new movement or infection starts to attack the ignorant, the weak, the young, and the thoughtless and gradually extend upward till they would become strong enough. He goes on to make it seem like slavery is an upgrade from the situation they were in Africa. He finishes off by making seem that things in the South were more under control compared to the North to make seem that allowing slavery was the reason. What is your opinion on this?

It is important to offer some clarification. The "incendiary spirit" to which John Calhoun refers is that of abolition, or the fervent movement to end slavery, which was dominant in the New England states. He refers to this in the previous paragraph in which he discusses the need to "[arrest] the progress of abolition." He also begins the essay with what amounts to a call of arms: "I do not belong...to the school which holds that aggression is to be met by concession." Interestingly, he asserts that those who do not meet "encroachments" at the beginning are destined "to become slaves." In other words, the South will not cede its way of life, but he also does not want to "[resort] to secession or disunion." His appeal in this speech is one for peace.
To your second point, Calhoun does try to make the argument that "the black race of Central Africa" is better off than before. He says that the conditions for the slave are better than those for the tenants of the work houses "in the more civilized portions of Europe." He seems to be referencing the work houses of the Victorian Era, usually inhabited by those who worked in textile factories. Calhoun claims that the slave has "the kind superintending care of his master and mistress," which allow for him or her to be looked after "in sickness or infirmities of age." 
Anyone with even an elementary knowledge of the antebellum South and the slave system knows that this is a lie. While it is true that not all masters and mistresses were cruel to their slaves, the very fact of owning another human being from birth to death, disqualifies any pretensions of goodness. Conditions for the poor in work houses were, indeed, abominable; and England's strict class structure offered little hope to escape from penury, but these laborers were still free. It is possible that some did have the opportunity to escape from their misery. No such opportunities existed for slaves who could only escape from their condition by running away, which was extremely risky and held no promise of freedom.
Calhoun justifies the plantation system by claiming that "never has yet existed a wealthy and civilized society in which one portion of the community did not, in point of fact, live on the labor of the other." He defends himself with history, while intentionally overlooking, like many Southern sympathizers, the unique project of the United States: to dismantle these ancient hierarchies and to create a nation in which "all men are created equal." 
He does, indeed, make the case that this "neo-classical" order -- that is, one that mimics the hierarchies of Ancient Greece and Rome -- protects the South from the kinds of clashes between ethnic groups which were common in the North at the time: "The condition of society in the South exempts us from the disorders and dangers resulting from this conflict [between labor and capital]."
Calhoun conveniently forgets the bloody insurrection that took place six years before when Nat Turner led a group of slaves to kill around sixty whites in Southampton County, Virginia. While it occurred in one small area, news of the insurrection rippled throughout the South and made slave-holding whites more fearful of future attempts. All was not "so much more stable and quiet" than in the North as he claims; and the stability that did exist was only due to the fierce determination of black people to survive. Clearly, black people were not content with their condition as slaves, but did not know how to get out of it without confronting mortal danger.
Based on what I have outlined, I think that you can form a sensible opinion of Calhoun's speech. His efforts to avoid discord with the North, while also defending the pride of the South, are somewhat noble. On the other hand, his justifications for slavery are dishonest, and rooted both in racism and simplifications of history.