It's far more reasonable to think there are other explanations than what effectively comes across as very negative intent from the beginning.

For example, they may have hoped or believed they could find a better business model over time, an alternative to the traditional ad models. Based on watching their various experiments since the day they got started, I can say for a fact they did try other things (two examples: Imgur as a service via paid API and Imgur Pro accounts).

Is it more likely the Imgur founder was naive or malevolent? The answer is extremely obvious.