You're, right, we'll have to agree to disagree.
Crazy people are gonna do crazy regardless. If you tell the anti-vaxxers that it isn't close to 100% (which would be false based on all the evidence that we have to date, and all the evidence seems to suggest that the effect gets bigger with time, not smaller), those people will be even LESS inclined to get the vaccine. So I don't see any value in equivocating on the effectiveness.