Again however the 50,000 runaway figure is only 1.2% of the 3.9 million plus slave population. That means even at this level 98.8% of the slaves didn't runaway.
If they didn't run north to obtain their freedom, what was their purpose for running?
While the runaway would most certainly blend in more readily with the general population in the south, than in the north, he would still have stuck out like a sore thumb, because the slave was a dependant personage that relied upon his master to provide for his needs. A slave going from place to place looking/begging for food and shelter, or stealing it as needed, or sleeping in the woods, would have certainly drawn the attention of authorities very quickly.
It would have been like the Japanese POW camps in Burma (Bridge over the River Kwai) There was no need of a barbed wired fence around the camp because the Jungle was an effective barrier in itself.
The same is true in the old south society. While a slave was an everyday sight, an out-of-place slave was easily spotted. This is why the Underground railroad was necessary to provide the food and shelter to assist the runaway. But, on the other hand the opperation of the railroad itself couldn't be so extensive as to attract unwanted attention. These conditions and the necessary secrecy alone would have naturally kept the actual numbers of successful runaways to a minimal number.
It would seem that the "runaway slave" and "Underground railroad", while it certainly did happen, most likely appears to be grossly blown out of perspective in order to justify a political objective. As the number of runaways that they could have assisted would be a fraction far less that 1 percent of the total slave population. I would estimate no more that 1/4 of one percent at best. That would still be 10,000 and that would have been a difficult number to sustain in hiding and move along a pipeline to freedom as it was.
The 2,000 runaways reported in the 1860 census, which I would classify as probably successful runaways, would have been only 1/5th of the 1/4 percent figure mentioned above. This would still repersent only 4 percent of all runaways attempts, if 50,000 total attempts per year is the figure we agree upon.
In modern day terms, there is a larger percentage of our children in todays society that runaway from their own parents before they reach the age of 18.
It wasn't the number of runaway slaves that upset the southerners with the Underground railroad. It was the fact there were people who openly disregarded and violated the law combined with the lack of enforcement of the law outside the southern states. That inflamatory set of circumstance is, in my opinion, what caused the lack of confidence in the government in general among southerners. And why southerners didn't believe a things Lincoln said.