It won't stop infection. But it greatly reduces that rate and, above all, your risk of death and the strength of the disease in general in case you do catch it.
> Convince them that it's necessary to stop the pandemic without giving any arguments.
The argument should be very clear: vaccines are a known and easy way to make the virus a non-threat, or a small one at that.
To that end, you can see the numbers for yourself after vaccination started[1] and how greatly the number of deaths and cases has reduced.
[1] see for example Brazil since June till now: https://www.worldometers.info/coronavirus/country/brazil/
> Have them defend your measures in public forums and feel very smart.
Given this is a place where IT Big Corp and govts. are constantly critized, I don't think anyone here is defending this as an WHO or any institution ass kisser