Properties are measurable.
In your scenario, half of the people believe wealth redistribution is moral while the other half do not. These beliefs manifest themselves - in part - by the type of government a region develops over time.
I answered by implying that the US government reflected the average you sought. It should serve as an accurate measure of the desired property.
Returning to my analogy using the concept of temperature, although the the rate of translational motion for a molecule is measured in units of velocity and the macroscopic unit of temperature (which reflects the average motion) is different, they still give a value that reflects measurements of the same property.
Practically speaking in terms of your scenario, the competing ideologies will each experience more or less short-term following until time has shown which is more superior and the tenets of the failing one are either wholly or partly abandoned. Until then, measurable properties of the system will reflect various ratios of the ideologies - half-and-half or some other fractional division.
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