The electoral college was put in place for the same reason the Senate was, to 'protect' small states from being powerless in the federal system, where the big states would have an obvious advantage in terms of the House of Representatives and any potential popular voting scheme for president. The smaller states (in terms of population) were, at this point, semi-autonomous political entities and while they wanted a strong federal government for the purposes of trade and protection they were worried about being made powerless in the federal system. Now it's definitely true that some of these states were smaller BECAUSE of slavery, since slaves weren't counted as whole people (the 2/3rds compromise was part of this bargain as well, of course) but it wasn't specifically about slavery. It was about federalism. I'd like to repeat that I am not trying to downplay the importance of the slavery issue ON the federalism issue, but the one is not subsumed in the other.
What this means is that even in the post-slavery era the electoral college still serves a purpose. It keeps the small states important on a national level and prevents the coastal states from electing presidents on their own. Wyoming has less than half a million people in it. New York City has more than 8 million people. Why would a candidate in a popular vote election spend time in Wyoming or make promises to the people of Wyoming when they could have access to nearly 20 times as many people in a much more concentrated area? The electoral college is the answer.
Now you might argue that presidential candidates shouldn't have to worry about Wyoming, at least not disproportionately to its population, and that's an argument with significant merit. The current system devalues New Yorkers and Californians while privileging people from Montana and Wyoming. Wyoming residents have 4.3 times the representation when it comes to the presidency that Californians have. This is inequitable.
It won't change though. The reason for this is pretty simple. In order to change the constitution you need ratification by the states. The electoral college gives power to a bunch of the smaller states. They wouldn't ratify an amendment to reduce that power. Case pretty much closed. Neither the governments nor the people of those states would allow their power to be taken, even if it made things more fair.
My point is not that the electoral college is a good thing, just that it's here to stay and perhaps more importantly it's not just an anachronism. It represents the point of view that the United States is STILL a group of individual states united in a federation and that each of those states is an entity with real value and importance. Thus it's Wyoming and New York that elect the president, not the people of the United States. I won't endorse or state the case against this point of view, but I think it's a respectable one.
The electoral college is not just an anachronism. It is something that, even if it is to be cast aside (which as I've said I find incredibly unlikely) must be treated as having serious arguments in support of it, since it does.