Ignorance plays a large role, but even when people are overwhelmed with (accurate) information, I'd say over 90% of people still take the cruel but easier path.
IMHO there's different kinds of ignorance. There's a difference between the absence of knowledge and misperception of reality. The first is an intellectual type of ignorance: the lack of information. The latter is the lack of wisdom/insight and leads to superimposing a view of reality onto reality itself, which leads to cruel behavior and suffering.