Your expectation of what upvoting and downvoting represents does not match up with the most intuitive psychological interpretations are - and therefore, it is unrealistic.
However, I will also state that while the problem you perceive is more relevant for comments, having up/downvotes represent Like/Dislike is more appropriate at the Thread/Post level - as the idea for a subreddit is that content users like should be promoted and content they don't want to see should be demoted.
That makes it even more difficult because now you want the arrows to mean different things depending on the area they are used.
You will never break the link between voting and Like/Dislike. However, what you can do is have a separate control to indicate whether a comment is appropriate or not.