If its not compulsory to have the vaccine that is not a vaccine...

If its not compulsory to have the vaccine that is not a vaccine why would we need a proof of vaccine certificate?
Would being refused service or entry to somewhere for not having one be discrimination?

A vaccine prevents one from contracting a disease & that is ok, I am all for it.
But being forced / coerced to have a needle that does not prevent one from catching the virus or potentially spreading it is just not right.