It wouldn't bother me if somebody wanted to bring a friend on a date. However, I would communicate that it would change the dynamic into a "hangout" over a traditional "date" for me. The difference being that a date carries romantic intent and a hangout is for the sake of connecting with others without romantic expectations. Also, a hangout means everybody pays for themselves.

This takes the pressure off by lowering the stakes since it's now just a casual hangout between peers. It also has the benefit of making the third not feel excluded as a third wheel but a welcome part of the group.