I mean, "opposite" implies some kind of continuum that they're both placed on. "Up" is the opposite of "down," it's not up vs. banana.
In this case, I'm comfortable saying that on the "bullshit politics I learned from the internet that sound clever but are in practice an instant disaster to anyone living through them" continuum, tankies and ancaps are like sugar and spice.
Edit: Oh no what have I done... I adjusted the analogy to a gender neutral one