For instance, you are incorrect that no slaves freed themselves--here's an example of a woman who sued for her freedom under the Massachusetts Constitution and won (lawsuits from other enslaved people followed--some won) - http://en.wikipedia.org/wiki/Elizabeth_Freeman_(slave)
There are plenty of other stories such as this, along with numerous accounts of escaped enslaved people, many of whom were not helped by the Quakers, but by other, unexpected groups.
The tone of your comment is also at turns appallingly dismissive--you write of enslaved people as being "fed and watered" and indicate that they were cared for. But numerous narratives make clear that slaves were often not fed and clothed sufficiently, not to mention that their health and hygiene was neglected. The idea that they were provided for adequately is a foolish and unwarranted assumption. They were treated, often times, worse than animals.
Not to mention the routine sexual assaults that women and men endured--that's in some of the narratives as well. And not merely an assault only from the slave owner, but from his siblings, sons, overseers who worked for him, and the like. A particularly noteworthy account observed that slave owners would interrupt the meals of enslaved families and require the daughters or wives to leave with them to be sexually assaulted and then return the women after they were finished. These would be severe horrors to anyone who had to endure them and can't be ignored because someone doesn't like to hear about them--or thinks something else is more interesting.
These enslaved people were human beings. There is no reason to minimize the suffering portion of the narrative, especially since they lived with those horrors daily and accounted for a significant part of their experiences while enslaved. Again, if you've read some of these narratives, you would know that there are lengthy discussions of their lives after becoming free--everything isn't about their suffering.
There are certainly other perspectives from which we can look at American slavery. The corrupting influence was (and remains) staggering.
Of course people like stories that challenge the narrative of the sufferings of African enslaved people. It is more pleasant not to discuss or even acknowledge the horrors that existed, for a variety of reasons. But these things did happen, and sites like slaverystories.org do a good job of illuminating not only the horrors that existed, but also the variegations of life and humanity.