A Question of Interpretation

I'm currently reading the Penguin edition (unfortunately abridged) of Darwin's Voyage of the Beagle. It's still early yet, but I'm enjoying it. (I was interested to find that one of the people involved in getting Darwin onto the Beagle was George Peacock, one of the unsung heroes of mathematics.) I just ran across the following passage, concerning a daytrip from Rio de Janeiro:

This spot is notorious for having been, for a long time, the residence of some runaway slaves, who, by cultivating a little ground near the top, contrived to eke out a subsistence. At length they were discovered, and a party of soldiers being sent, the whole were seized with the exception of one old woman, who sooner than again be led into slavery, dashed herself to pieces from the summit of the mountain. In a Roman matron this would have been called the noble love of freedom; in a poor negress it is mere brutal obstinacy.

I find myself hoping that that last sentence was intended ironically, but fearing that he was quite serious. The passage is dated from 1832; Darwin was twenty-three years old.