For a UK citizen to be able to work in, say Austria, and be immediately entitled to whatever benefits that local workers in Austria are entitled to is to me the same as a worker originally from London going to work in Glasgow or Cardiff. It turns all the countries into sub-regions.
Yes, it is a choice of a country to veto, but then look at all the consequences built into doing that (as we have seen with this whole Brexit referendum situation).
It would make more sense if all the systems of employment and tax revenue were the same but they are not (most if not all countries naturally have different government and economic histories that have evolved over time depending on what has happened in the countries to shape them). But this rule whereby to have a common market you must have totally free movement within plus commonality in worker benefit entitlement from day one is what ultimately forces the common market into one unified European nation state (by proxy).
I don't see why we don't have common market trading rules with preferential movement for citizens within the zone, but without movement by citizens within the zone having to be totally 'free'/'uncontrolled'