Well, there will be soon be an official retort / react style plugin where you can react to posts with any emoji, or a specific predefined set of emoji. So you could
- hide all the like UI elements via CSS (this is possible, I know one Discourse instance that does it)
- install the official react plugin and only whitelist the up or down thumb emoji reactions
But as far as project goals and philosophy, we at Discourse are ideologically opposed to downvoting / dislikes – and I don’t see that ever changing. If downvoting is a hard requirement, you should look for different free / open source software that meets your specific requirement.