Not the OP, but while I'll agree with your sentiment in general, it's a bit straw man argument in this particular case.
I'm generally of liberal persuasion. I did not agree with almost anything that our Canadian previous conservative prime minister did... but I respected him. I thought he was intelligent, effective, and thoughtful. I didn't like that he was effective and productive about things I disagreed with, but I'd shake his hand and I can imagine having a thoughtful conversation and learning something, even if my mind may or may not be changed.
On the other hand, in theory, I "agree" with many of the things Michael Moore for example is fighting for. But I do not respect him, and I cannot watch more than 2 minutes of his programs before wanting to yell at the TV. Certainly, I wouldn't elect him. He is a propagandist, he cherry picks data, and presents a skewed picture. Ann Coulter or Glenn Beck or Michael Moore or Al Franken (the pundit; he may or may not have been more honest as a politician, but his prior books were awful) - it's not a matter of how much I agree with them, but that I find them all fundamentally dishonest.
Which brings us to Trump - my biggest concern is not that I disagree with him (which I do). It's that I have no respect for his mental faculties, honesty, abilities, consistency, beliefs, values, thoughtfulness, or any of the characteristics some of us believe a head of state should have. Further, I think not only is he doing a disfavour for those who disagree with him, I think he's doing a disfavour for those who agree with him / voted for him.
At the end of the day, I may disagree with somebody about what's the best colour to paint the room; I may disagree with somebody on what the best way to fix a education system is, or even what its goals should be; I may disagree on budget priorities, on a country's role in the world, and so on. There's fascinating discussion, debate and learning to be had with people of opposing opinions.
But if somebody wants to buy a bridge somebody's selling them, enroll in a cult, or jump out of an airplane without a parachute thinking it'll end well for them, dunno... I don't think it's in the "difference of opinion" category :|