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Indeed it is. Zealots treat limits as a foot in the door.
Witness the shipping industry and fuel sulphur.
Marine fuel has sulphur upto about 4.5%.
In an attempt to reduce SOX emmissions close to shore and in order to finally ratify the MARPOL ANnex VI treaty they agreed that within ECAs (emission control areas) 1.5% limit would be fine. This meant that low sulphur fuels were preferentially used in ECAs and high sulphur fuels at sea (the motive is health.
This was based on what was available and achievable.
Now the limits are being pushed down. There isn't enough low sulphur fuel and to make matters worse they are pushing down the global limits as well.
There is no chance of removing the sulphur so the shipping industry is now considering LPG, Biofuels and Diesel. All in competition with land uses for those same fuels. And all at about double the price. Since fuel is 60-80% of operating costs the consequences will be severe, the benefits negligible (except to a few people in rich countries with long life expectancies already some few of whom living close to the sea and shipping lanes, might get a week or two extra life. On the other hand, those poor people with short life expectancies, poor nutrition and no health care will suffer when exports will become too expensive and they will move deeper into poverty and malnutrition. (Not measured and of no interest to the eco warriors, neither who benefits nor who loses because it isn't about the environment nor about peoples life quality).
I can actually think of an exception to "...once zealots have established a limit, it is never increased..." The zealots and limits I'm thinking of are population control zealots and their proposed target for the UK population size.
Back in the 1970s and 1980s the UK Greens, or at least a substantial proportion of them, proposed that the UK population should be cut by 20 million, which would be equivalent to the UK population target being 35 million (assuming the population was about 55 million at the time). This Wikipedia article mentions the 20 million cut figure:
I've got a feeling the 20 million figure was official Green/Ecology party policy at one time, but the Wikipedia article gives the impression that the issue only came up in 1989 and was never accepted as party policy. However I think that the figure counts as a limit established by zealots.
In the present day the main pressure group for UK population control is the "Population Matters" organisation (formerly known as the "Optimum Population Trust") whose activities are endorsed by 'distinguished patrons' including David Attenborough, Paul Ehrlich, James Lovelock, Crispin Tickell, Jonathon Porritt and Chris Packham. Their website is: http://www.populationmatters.org/
Their proposed UK population target isn't easy to find on the website. You have to follow the links: About > Campaigns > Call for an end to population growth
The last sentence in the 'Call for an end to poulation growth' article is "For the UK, we ask the government to commit to keeping the population below 70 million."
This 70 million target population figure (which is higher than the current population of about 62 million) represents a doubling of the population target the Greenies wanted over twenty years ago. The Labour government (Phil Woolas) actually accepted the 70 million cap back in 2008, but the Coalition government (Theresa May) rejected the cap last year.
The current position of the Green party is that they have no population target, as the Lefties that now dominate the party do not want to offend immigrants (the people most likely to be affected by a population control policy) in any way. Also there isn't a UK-wide Green party any more - it got split up to take advantage of the tendency for the Green vote in Scotland to be nationalist.