The issue is not that they were working from false assumptions, or drew bad conclusions. In science, this isn't a crime, just a mistake, and it happens.

The issue is that the environmentalists and some politicians were all set to drastically alter our society based on this incomplete information. Had we done everything based on the assumption that food supplies were going to collapse as soon as 1985 (which they didn't), what do you think would have happened to our economy? Stockpiling food? "Y2K" ring a bell? Never mind melting ice caps.

The accuracy record of the doomsayers, like Paul Ehrlich and the "Club of Rome," has basically sucked from day one. The problem is not that they are making rotten predictions, the problem is that they want to run our lives based on them. Without any exception I have ever been able to find, all of their "solutions" to their predicted disasters involve a massive increase in central government power, and a reduction in the freedom of the individual.

Many people act as though this is no big thing, and that changing our society on the basis of an educated guess has no real costs to it. This is usually expressed as something like, "shouldn't we /reduce our industrial output/outlaw the internal combustion engine/stop raising cattle for meat/restrict families to one child/ just in case these people are right?"

A little light reading on the subject.