Voting on meta is different:
Note that voting on Meta.stackoverflow.com works differently from the other Stack Exchange sites. Voting is used as an expression of agreement or disagreement on contributions here, rather than to point out a lack of quality or helpfulness. Do not be too concerned if you receive downvotes - it is possible that members of the community are simply disagreeing with what your contribution is suggesting.
In addition, and for this reason, voting on meta doesn't affect 'rep' at all.
Most folk who participate on meta already know the ropes on the main site and/or are active in chat, so it's easier to communicate the above to them. It's still helpful to mention this in a comment from time to time for new meta users, but generally you shouldn't have any qualms about down-voting answers you disagree with here.
If you are still not sure, consider that the folk who up and down-vote effectively have twice the say you have because they have twice the amount of influence on the way posts are sorted overall. And that's not very fair :)