So the only rating available at the moment is the heart. Which basically functions as agree did in the old forums (although you are rate limited in the number of agrees you can hand out per day by your account’s trust level - for more on this see this: https://meta.discourse.org/t/what-do-user-trust-levels-do/4924 )
We could potentially add others but only if there is a good case for them serving the purpose of building the community or building the informational quality of the forum. As they were in the original forums ratings were a feature that were largely abused.
People manipulated them to artificially boost their account in gamified elements of the forum (ie they incentivised shit posting) and they were used as a substitute for actual communication - as you point out to passively aggressively show disagreement without explaining your viewpoint, engaging or justifying what you were saying.
On these forums there are a number of badges which are set up to incentivise good forum behaviour (such as the helpful badge for those answering questions in the Help! Category) - and for most of these you can collect them multiple times so if you want a gamified forum experience - there it is. However most are set up so that their limit is based around quality rather than quantity.
TL:DR Basically we want as a community less of these 
and more of these 
and its not clear that ratings in the old forum were encouraging that.