Carbon credits serve a pretty obvious purpose, and if any of you guys had done 4 seconds of research before forming an opinion (I know, I know, that's crazy talk), you'd know that. In fact, while it's "capitalists" who frequently scoff at carbon credits, they are actually the most reasonable method of controlling pollution without destroying the economy.
See, the problem with applying mandatory pollution standards to everyone equally is that everyone is NOT equal, not all industries or individuals can reduce their own pollution below a particular limit, while others can reduce their emissions well below any reasonable limit. If there was just a limit for output, you'd have to both deal with companies that emit too much and you'd have no way to give an incentive for anyone else to reduce emissions below the legal limit. Carbon credits solve both those problems, the end result being a system where people are given an incentive to reduce emissions as much as possible while giving some leeway to those who can't.
A simple example, company A and company B. Both pollute as part of their core business, but for various reasons, company B can reduce their emissions a lot more than company A. Now let's say we want overall emissions to be about 1000 tons per year per company, on average (totally made up numbers) and both companies currently emit about 1500 tons per year per company.
So in the non-carbon credit scenario, we set the legal limit at 1000 tons per year per company and enforce it through fines. Company B can easily reduce emissions to 1000 tons per year, which they do. Company A, on the other hand, struggles to reduce emissions to 1250 tons per year. They keep getting fined for not meeting the limits, and so either through fines or an effort to meet the limits, they spend a lot of money on their excess pollution and end up with a damaged business. Overall, we have an average of 1125 tons per year per company, and we've hurt one company.
WITH carbon credits, it's a different story. We set the legal limit, but this time allow company A to buy carbon credits to make up for their shortfall. Company B now has an incentive to reduce their emissions below the legal limit so they can sell company A their excess credits. So company B reduces their emissions to 750 tons per year, and sells the excess 250 tons of their allowance as credit to company A for cheaper than company A could reduce their emissions by that much. We now have 2 economically healthy companies, and an average emissions of 1000 tons per year per company. On both the environmental and capitalist fronts, we come out ahead.
The objections to carbon credits almost always look at one side the equation only, the amount the excess polluter is putting out. They dismiss carbon credits as some BS trying to magically spirit away the very real pollution without looking at the fact that there are a fixed amount of carbon credits in the system, which means the total amount of pollution remains the same. Only instead of trying to force every single company into the same box, we've created a more efficient system where the companies that are best at reducing pollution have an incentive to reduce it the most.