He's too 'decent', so he could forgive anything and let the bygone merely as bygone... that's my take of him
Hmmmm that could also be another way to see 'decent' as. Interesting view ^o^
another point for consideration is that He's not the one who actually experienced the abuse for prolonged time, so He could 'easily' said that lines.... (most people did)
Another somewhat realistic POV -from physiological POV, at the time Ethan was just a kid, meaning his psyche, mentality, and personality was being built, and plentily susceptible to external influence... so any high level of stress would leave a long lasting effect -kinda like a trauma; while on the other hand the old was already an adult... he has finished his 'inner' side, so if he was raised 'decently' then it's no wonder... XD
Yes I agree with you especially on the part that the professor wasn't the one who really experienced it. Also, maybe the professor did not know how much Ethan was abused and he seemed close with the father...
"FoRGivE yOuR fATheR" Damn I thought the professor was gonna be a decent person