That comparison doesn't really work. Obama's place of birth is a checkable fact, not an opinion about whether or not a particular thing is good or bad.
I agree totally with CRI, but it's not just because he's black. It's because his mother was a white academic who had a child with a black man, and an African at that, then he grew up in Hawaii, which is barely America, surrounded by academic types. He's a mixed-race intellectual with a funny name and a foreign father. He's already under suspicion - his place of birth is but the detail that confirms it.
Yes, I don't think you can compare the two (and imo, any measure that affords basic human rights to those who've been denied them
does represent an advance of civilisation.)
It's important not to underestimate how endemic white supremacy is in many quarters in the US. Not that much time has passed since overt segregation was legally enforced (not just the No Blacks, No Irish, No Dogs version in Britain,) and the desire among some to return to that "golden age" where black, brown, red and yellow people people (and women, and gays, and disabled people) knew their place and didn't complain. Most know logically that their bigotry is irrational, so they seek out and cling to pseudoscience, way-out theories, factoids and/or religious faith in hopes of creating some plausibility for their views.
So, the argument would go something like this. You can't have a Black president, because Black people are lazy, dishonest, immoral, greedy, volatile, stupid and threatening. When someone like Obama comes along, who defies all those stereotypes, it blows their minds, because it completely undermines everything they believe about the "right ordering" of the world. That's why they've gone to extreme lengths and embraced preposterous arguments to try and delegitimise his presidency. Even his actions or policies that benefited them (e.g. Affordable Care Act) made no difference to their views.
May sound far fetched, but I think some were still so furious at having had to "endure" a Black president, they threw their support behind Trump, who's effectively a poster boy for laziness, dishonesty, immorality, greed, instability, stupidity and threats cause hell, at least he's a white guy. They've nailed their colours to his mast so even as he leads the nation down the swanny and the world quite possibly to war, they're still backing him, even if that means their self-destruction. They really are that furious.
And of course some among them are praying for the rapture, and the more incompetent his leadership, the more likely that will happen, and soon.