This question really depends on context. The average person where? In the South most people were well aware of the realities of slavery. It was, in fact, a major building block of societal norms. Even though not everyone owned slaves, they would have seen them on a regular basis. We have this image of slavery as something like a concentration camp, with the slaves laboring away on the plantation, but this is a bit misleading. Obviously, most slaves worked on plantations, but even there slaves were a lot more mobile than people tend to think. Slaves slipped away to visit friends and family on other plantations, sometimes with and sometimes without the plantation owners' permission. Slaves sometimes grew their own small plots of land for extra cash or did odd jobs around the area. There was an entire "black market" economy in many areas, with pubs where you could find slaves and poor whites drinking in the same area, though not necessarily as friends. Additionally, many slave owners rented or hired out their slaves to small farmers for weeks or even months at a time. A small minority of slaves were even allowed to rent themselves out, with their owner keeping a share of their pay.

In cities the situation was even more complicated, as some slaves were allowed to live by themselves. In cities such as New Orleans there were large populations of free African-Americans as well. New Orleans was also home to one of the largest slave markets in the country and throughout the South it was not uncommon to see the march of slaves as they were bought and sold in the internal slave trade.

Additionally, slave patrols regularly crossed patrolled around the South, actively looking for runaway slaves. Slave patrols were largely a part of the militia, so most men would have participated in that at some time or another.

Outside of the South the question becomes more complicated. In the North during the early republic there were still a few states that allowed slavery, though for the most part they died off fairly quickly. In the case of New York, the state legislature introduced gradual emancipation that went into full effect in 1827. Even after that, however, southern plantation owners travelling through the North often brought their personal slaves with them, in the most famous instance leading to Dred Scott v. Sandford, where a slave who had lived in the North for some time sued for his freedom. So, Northerners would have been at least slightly familiar with slavery as it existed at the time.

Interestingly, one area where your meat industry comparison makes a lot of sense is in Great Britain. Great Britain held many Caribbean sugar colonies at the beginning of the nineteenth century and sugar was naturally very popular among the common citizens. Most citizens in Great Britain never saw the horrors of slavery and it was a classic instance of "out of sight, out of mind." Abolitionists in Great Britain went to great efforts to bring slavery back into the mind of British citizens. They created pamphlets and posters with slogans such as "sugar made with blood" to highlight the brutality of the sugar industry.

To get to the other part of your question about attitudes regarding slavery it is once again a complicated area. It depends not only on where, but when, you are looking. In the eighteenth century slavery was frequently looked at as a somewhat distasteful economic necessity. This attitude was common among Southerners, perhaps most famously Thomas Jefferson. However, once the abolition movement really got going, first in Great Britain, then later in the US, Southerners doubled down on slavery and began claiming stridently that slavery was not only necessary, but a good thing for both slaves and their owners. They regularly characterized African Americans as inherently lazy and stupid, who need the "paternal" guidance of their owners to see that they did something productive with their life. Southerners who did not own slaves also bought into this ideology for the most part. Southern society was very hierarchical and the reliance on slavery meant that even the poorest white men was socially higher than slaves. Of course, this consciously projected image was at regular odds with reality. As you point out slavery was brutal and there's no getting away from that fact. However, the image of slaves as lazy and stupid and possibly even subhuman was spread far and wide. There were few abolitionists even in the North who would have said that Africans were the absolute equal of white men. In many cases abolitionists claims were based on a free labor argument and on the belief that slavery was making white Southerners more bestial and less civilized, rather than out of concern for Africans. This belief persisted through the Civil War, where government officials feared that freed slaves would become permanently reliant on the federal government for support, rather than going out to work themselves.

This is a very brief glance at the attitudes regarding slavery and I've left out the various attitudes that existed in the rest of the western hemisphere, most of which had also utilized slavery at one point or another. The Spanish empire relied heavily on slavery and the Spanish colonies, former and current, had their own societal views of slavery. But, I hope this helps to answer your question and get at a hugely complicated topic.

Further Reading (good lord there's a lot): Franklin and Schweninger, Runaway Slaves, Genovese, Roll, Jordan Roll, Johnson, Soul by Soul, Johnson, River of Dark Dreams, Buchanan, Black Life on the Mississippi, Williams, Capitalism and Slavery, Brown, The Reaper's Garden, Curtin, The Rise and Fall of the Plantation Complex. If there's a particular topic that interests you I can make some more specific recommendations.