Unacknowledged or unmarked quotes are plagiarism, plain and simple, and they deserve the full weight of community displeasure to be heaved on them: comments, downvotes, and eventual deletion.
On the other hand, if an answer consists completely of well-acknowledged quotations then it deserves to stay on the site - it's not doing anything against the rules, so deletion is not appropriate. In general, though, such answers are of very low quality, and do very little to actually address the problem, so they deserve what all bad answers do: to be downvoted into grayness, with comments expressing this displeasure.
There are indeed cases where "something is so complete and well-written to begin with" that it would "make it worse" to require the poster to paraphrase it, and if that's the case - the quotation is completely on the mark that it fully answers the question in a self-contained but well-referenced fashion - then kudos to the poster and an upvote for providing a useful answer.
Otherwise, though, I say let votes show that we don't like this.