How utopianism can avoid becoming dogmatism.

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.

Didn't Plato say something to the effect that the ideal can only be ideal in imagination, before reality can corrupt the ideal?

That is pretty much what Plato said. It been a while since I read the Republic but I know he devotes a section to what the purpose of the ideal is. He had his theory of the ideas which is where he goes into how reality can corrupt the ideal if I remember correctly or I may just be linking two different but related ideas.

Aristotle talks about how everything living has a lifespan in which it is always changing towards its better potential or worst potential. Thus, as soon as a society is deemed to be a utopia the society quits working towards its best potential and thus can only begin to degrade. The utopia is the community that adapts to the conditions of the environment to the betterment of both all individuals within the community as well as the community as a whole.

Utopias assume that their conditions are so self-evidently perfect that no one would ever dissent. But that's the catch -- no utopia makes a provision for dissent, including dissent that would take down the system.

Unfortunately leaders with strong armies and utopian visions never figure this out until they send masses to the Gulags, the gas chambers, or the Killing Fields.

It's no utopia if I can't dissent. Even if everything was perfect, I'd complain - just to keep the leaders on their toes.

And any time mass murder is involved in a utopia, the advocates of said utopia have drifted into madness, if they were not mad to begin with.

Yes, utopian thinkers undermine their own position quite often by prescribing a status quo that is "acceptable". There is no utopian ideal, so to speak, as human nature and values are not static and are certainly not absolute. This is why I advocate a dynamic and destructive form of society, a constant state of anarchy.

It should be noted that self-proclaimed anarchists are often the greatest offenders of this utopian thinkers, but I differ from many in treating anarchy as a means and not an end, as a process and not a finished product.