How large?

According to Gallup, 16% of white Americans disapproved of interracial marriage in 2013 [1], which is probably the closest you're going to get to a major poll asking about apartheid.

[1] http://www.gallup.com/poll/163697/approve-marriage-blacks-wh...

Considering 20% of Trump voters think freeing the slaves was a bad idea[0], I'd say "a lot".

[0] http://time.com/4236640/donald-trump-racist-supporters/

I looked for information about the poll but the page you linked and the linked page within the relevant section both appear to lack that information. The 20% is an approximation, apparently.

It seems the question was:

Should "the executive order that freed all slaves in the states that were in rebellion against the federal government" have been made, or something similar. Was that worded badly on purpose, it appears to say "is freeing people who are rebelling against the government good"?

I find the statistic hard to believe, such a claim needs careful support which is lacking. The details that are given suggest an opaque question.

Such questions need follow-up questions to gauge understanding and depth of sentiment. Anyone who asks that and doesn't then ask 'so should the slaves have been freed at all?' as a follow-up is most likely being deceptive.

Thanks for looking that up, I was immediately suspicious of that number. Way for somebody to conflate the complex geopolitical question of exactly which slaves to free when while in the middle of a civil war with the question of whether the slaves should be freed at all.

I'm guessing it's "yuuuuge".