If you’re the admin, you can create a theme component to hide it site wide with CSS (you could also apply it to a set of categories with a bit more work). You could allow users to choose their theme which would give them the ability to choose whether they want likes. Perhaps your can do it yourself if you see Developer’s guide to Discourse Themes.
A plugin would let you have a single theme and allow users to set a custom field that would turn it on and off. It would be about twice the work and make your site somewhat more difficult to maintain.