Analogies are useful for explaining the issue to people who don’t have the same background. There’s no single best analogy, so it’s useful to have a few to choose from when the need arises.
The swpat.org wiki has links and summaries of analogies based on minefields, literature, and music: http://en.swpat.org/wiki/Analogies
Comparing software development to road transport, software patents are like toll booths, at best, and road blocks, at worst. A toll booth is property, and it’s profitable for someone, but these factors don’t imply it’s in the public interest or in the interest of the economy as a whole.
Some toll booth owners, for whatever reason, would simply leave their toll booth closed, refusing to grant access, making a government approved road block. Others would charge some types of people to pass, and would block other types of people. Road users just have to accept this.
If the government opened a toll booth office similar to a patent office, granting permission to build tens of thousands of toll booths per year, road transport would be ruined. The toll booth office, getting paid for every granted toll booth request, would of course say the system is a massive success and that the criteria for excluding certain areas from having toll booths should be interpreted as narrowly as possible.
The toll booth office could even organise public consultations. They could inform all their customers – the toll booth owners – and they could generally rely on the fact that toll booth lawyers are aware of and do participate in these consultations, while road users generally don’t. The result would be a consultation which looks fair, but which systematically leads to endorsing increasing the number of toll booths on roads.
The lesson is that the opinions of patent holders and patent lawyers should be collected separately. The effect on software users and software developers should be much more important and the old “public consultation” method is completely inappropriate for this.