From what I have read George Whitfield did not support the harsh treatment of slaves by white slave owners. It is documented that he preached against harsh treatment of slaves.
He did own slaves but it is said he treated them well. It was also said he did not fight against slavery but that he did preach to slave owners and rebuke them for harsh treatment of their slaves.
At the end of the day George Whitfield loved GOD and shared with others the need to live a holy life before GOD. No man is perfect. We should always look to the LORD JESUS for our guidance. GOD uses men but our focus and eyes must be fixed upon the LORD. Slavery was a terrible ugly part of our countries history and truth be told it should have been dealt with from the beginning of our countries forming itself. However money and greed allowed for more compromise.
Here is a letter written by Whitfield and published by Franklin. In the letter Whitfield rebukes those who mistreat slaves openly.
n an open letter, published by Benjamin Franklin, to the inhabitants of Maryland, Virginia, North and South Carolina, Whitefield wrote the following:
‘I must inform you in the meekness and gentleness of Christ, that God has a quarrel with you for your cruelty to the poor negroes. Whether it be lawful for Christians to buy slaves, I shall not take it upon me to determine, but sure I am that it is sinful…to use them worse than brutes.’
‘Some, as I have been informed by an eye witness, have been, upon the most trifling provocation, cut with knives, and have had forks thrown into their flesh: not to mention what numbers have been given up to the inhuman usage of cruel task masters, who by their unrelenting scourges, have ploughed upon their backs and made long furrows, and at length brought them even to death. I hope there are but few such monsters of barbarity [among you]…
An uprising amongst the slaves would be just
Whitefield continued, ‘Although I pray God the slaves would not be permitted to get the upper hand [ie, in revolution against the white slave owners], yet should such a thing be permitted by [God], all good men must acknowledge, the judgement would be just.
‘Whilst I have viewed your plantations cleared and cultivated, and have seen many spacious houses, and the owners of them faring sumptuously every day, my blood has almost run cold within me, when I have considered how many of your slaves have neither convenient food to eat, nor proper [clothes] to put on, notwithstanding most of the comforts you enjoy were solely owing to their labours…
‘Go to now, ye rich men, weep and howl for the miseries that shall come upon you [for] their cries have come into the ears of the Lord…’ (Quoted in Arnold Dallimore, George Whitefield, Banner of Truth edition, Vol 1. P,495-6)