Very late to this series, but I just finished watching Total Forgiveness and I can't help but feel the utmost sympathy for Grant.
I think he was definitely naive throughout the show and is responsible for a lot of what happens to him, but Ally was consistently behaving in a mean-spirited manner. Particularly with following up the Flea Market fiasco with a degrading Performance Art challenge. They knew this was a man who had nothing, no earthly possessions whatsoever remaining. You cannot be more desperate and low, and in that moment they gave him a challenge that was truly beyond pale just so they could force another loss and make more money.
Warning - Spoiler for Total Forgiveness finale:
spoiler
I think the worst part of this show for me is the Finale. I've seen the reunion episode and I know that all has been forgiven, but I think Ally was incredibly manipulative here. After weeks of torturing and humiliating Grant, they finally pushed him to the edge. They knew he was angry and wasn't playing nice anymore. The challenges he was thinking of were truly horrible and on-par with what he felt had been done to him (he mentions challenging Ally to go to a conversion camp, for example). Rather than accept the monster they have created and play the game at the level they expected Grant to play at, Ally insists that their challenge is done before Grant publicly commits to his challenge. This breaks the rules of the game as we know it, and means Grant is open to influence in his decision for what Ally's final challenge is.
They butter up Grant with a nice day out so he is less likely to choose the extreme option. Grant, being the kind-hearted and naive soul that he is decides to not torture Ally for the finale. Ally then gets to play the nice guy by throwing the challenge. But if they had played the game fairly, Grant would've suggested something extreme, Ally would have refused to do it as they did with the snake challenge and Grant would have won the money anyway.
I think Ally has gotten away with being really shitty throughout this series. I was deeply moved by their diaries, and they were one of my favourite cast members in the old sketches, but I have come away with a very poor opinion of them, even after seeing everything is all smiles at the reunion.
ETA: Spoiler tag
This series was a chance for them to experiment with the format, but they made it very clear that this was largely in the hands of the players. It was also transparently experimental, which they probably had to portray because they saw how much the players were both impacted.
There is the context that the challenge the week prior to the flea market ,Grant had opted to challenge Ally to be drunk for the full week. Ally would have been thinking about the next weeks challenge of the flea market when they would have been in a compromised state. I think that Ally took this a bridge too far, and when that was clear talked with people they trusted and took a step back.
That said I don't think Grant was focused on just trying to make good TV, and was getting frustrated when Ally had actually gone through with challenges that he thought they would opted out of. Grant also had the only challenge that resulted in a permanent body modification through the form of a tattoo of Ally's girlfriend's name, and had Ally read their childhood diaries as an event at a book store.