Oh no, I didn't mean in regards to the rape specifically. The series heavily implied that Riddle Sr. was a pretty big asshole (along with his parents) well before any of that, though. Goblet of Fire, when describing the murder. puts it as the Riddle parents being snobbish, stuck-up, and pretentious and "their adult son Tom was, if anything, worse". He didn't deserve what happened to him, but he also didn't seem like someone who the reader would have liked, had we known him.

The part where he was pitiable was Merope drugging him into loving her. As you said, he did not consent to any of it and didn't owe Merope.