What is the common understanding that Landrieu is asking his audience to come to?

To literally put the Confederacy on a pedestal in our most prominent places of honor is an inaccurate recitation of our full past.

it is partly in consequence of such facts, that slaves, when inquired of as to their condition and the character of their masters, almost universally say they are contented, and that their masters are kind. the slaveholders have been known to send in spies among their slaves, to ascertain their views and feelings in regard to their condition. the frequency of this has had the effect to establish among the slaves the maxim, that a still tongue makes a wise head. they suppress the truth rather than take the consequences of telling it, and in so doing prove themselves a part of the human family. if they have any thing to say of their masters, it is generally in their masters' favor, especially when speaking to an untried man. i have been frequently asked, when a slave, if i had a kind master, and do not remember ever to have given a negative answer; nor did i, in pursuing this course, consider myself as uttering what was absolutely false; for i always measured the kindness of my master by the standard of kindness set up among slaveholders around us. moreover, slaves are like other people, and imbibe prejudices quite common to others. they think their own better than that of others. many, under the influence of this prejudice, think their own masters are better than the masters of other slaves; and this, too, in some cases, when the very reverse is true. indeed, it is not uncommon for slaves even to fall out and quarrel among themselves about the relative goodness of their masters, each contending for the superior goodness of his own over that of the others."