One of the problems that sometimes happens in books and stories that are heavy on allegory is that the writer forgets that not all the characters should feel the same way about the issue.
For example one of the few episodes of law and order I have seen was a very thinly veiled anti-gun message. The things was that every character felt the same way about the message, that guns were bad (for anyone who was not law enforcement obviously) to carry.
Even if most of them feel that way, having everyone have exactly the same views on a contentious issue just does not make sense. Even if they feel in general the same maybe one thinks that pistols are okay, but nothing larger. Maybe another thinks that anyone who goes through a long training process and has no criminal history is okay. You could even have two people agree on the end result but disagree on why.
It can come off as trying to pass off an opinion as a universal fact. Done well an allegory convinces people by letting them see a new point of view or by the use of reason.
Allegories don’t work just by having all the main characters say they feel the same way about an issue.
There are several things that are often shown when a writer shows a utopian future, several things that sound good but just don’t work.
The first is population. Often you see the earth with a much lower population. Humans are like water, we tend to fill any container we are in. Once you start to eliminate the reasons for having small number of kids a great many people will start to have more.
The main limiting factors for how many kids people have are time and money. If your in a future where the money needed to support you and your family takes little time to get then you would have as large of a family as you want.
If even things like daycare are cheap then I would think you would start to see larger families, not smaller ones.
The second is lack of crime. While true, if poverty was a thing of the past crime would plummet, but it will never go away. You will always have people looking for a thrill, or who would rather steal then earn luxuries.
Third is money. I know I have said it before, but I can’t see any way for humans to live without some form of money. Every time I see a plan for it it’s either just another name for money.
Humans have shifted how we think on a basic level many times, this is one thing to understand when writing anything set in the far future. If you want to show someone in the year 3,000 AD you need to try and think of how he will be different, not just in body but in how he will think.
To explain what I mean I will detail out a few paradigm shifts we have gone through.
The first is the age of enlightenment in Europe. The short explanation of this is that it’s when we changed from assuming things that we did not understand were supernatural to assuming they were understandable scientific phenomena. This sounds simple but it is not, it changed everything about our civilization.
The second is who people identify with. In a very real sense civilization happens when people decide they belong to more then just their family. At first this might mean their tribe, but then it grew to a city, and the city grew to into a nation.
What shifts do you think will happen in the future? Could we even accept them today if someone came from the future and told us about them?
An impression I get sometimes is that people think you need to be an expert in a dozen fields to write good science fiction. That simply is not the case, I would say there are two areas you must be conversant in.
The first is of course science. You do not have to be a scientist, you need to have a firm grasp on the science you are using, and be willing and able to research the details you don’t know. Never forget that the science can lend you plot points, a greater understanding helps you do more then just make a realistic story.
I advise you to at least get to the point you know what is and what is not possible under our current understanding of science. Even if your talking soft sci-fi you want to know what you can just handwave as easy (say a supersonic aircraft) and what you need to put some thought into (how FTL works in your setting) can make a big difference.
The second, and it was almost the first, is history. Knowing history does two big things for you. First you gain an understanding of how human societies work. For example we know that large scale communism does not work, every time it has been tried it has failed badly. This means if you wanted to have it work in your story you would have to know and address why it would work in your story but not in history.
The second thing it gives you is a grab bag of idea’s and concepts that have been done before, and that you know work. For example if you wanted a large scale empire that ruled for a long time you could look up examples from history, and either base if off one or combine them. In the least you would know what to and what not to do.