How grandpa would've reacted to Clark's secret?
If Martha and Jonathan let him spent anytime with them.
I feel like he would've either died of a heart attack, or become a much more open minded person over time. He was such a my-way-or-the-highway kind of guy, and so set in his ways. I think Clark could've changed all that for him. Opened his heart a little. And definitely let him see Jonathan with a newfound respect and admiration.
shareProblem is they didn't know if they could trust him due to their long history of disagreements, too much of a controlling father figure, putting his ways over what his daughter wanted.
Could've saw Clark as a threat to his daughter.