To my mind utopia is simply a reason for persons to improve their ethics and consider proactive activity - that in order to achieve utopia it is required for one to act in a specific fashion that would incur utopia.
Theory is an enemy of utopia, for like you've said there is a difference between utopia and dogmatic system; at least in my mind, for utopia to exist, coercion and dogma would not interfere with an individual's activity, for the activity would not harm another's existence, so reducing any need for dogmatic preventative measures. I think what utopia really depends upon is an ineffable theory of satisfactory and unharmful interaction and activity within a society, if achievable then the society could function in anarchy without ever becoming harmful to individuals within it - so dogmatic legal structures would be unnecessary.
However, the dogma of 'what is harm' or 'what is satisfaction' means that utopia will always be founded upon dogma, although it is possible for dogma to remain as a foundation and not interfere with the existence of the utopia.
Of course these examples (harm / satisfaction) are my own opinion on what a utopia could be, and I do believe that it is possible for a utopia to exist without any foundation of rationale co-opted with it's existence.