That isn't really true. The actual IPCC is a tiny UN group, around a dozen people, but the bulk of the data is compiled by unpaid (well, unpaid by the UN) scientists who participate in working groups that argue over the science - it is not without some flaws. They use geographical and gender parameters for participation so a working group may not have the best scientists in the world, some will have been chosen because they needed to meet a cultural quota - and they still get to be heard.
Climate science is a political issue, which leads to concern about who gets chosen (or thrown out, in the case of the 2001 report) and what data is used. Estimates are made using numerical models which, like the working groups themselves, vary in their credibility. People now know that some of the data a group chooses to use may not have been published at all, much less peer reviewed. As an example, no one outside the IPCC and corporate science media and those inclined to accept any claim that implicates humanity believed the Himalayan glaciers would be gone by 2035 just because someone in an interview once said so - though that 'data' was in the 2007 IPCC report - nor did anyone seriously believe African farmers were going to suffer 50% yield drops by 2020 due to global warming - both were too outrageous to accept and it just made the IPCC look bad.
Yet on the other side were people complaining the IPCC was underestimating sea level rise when they predicted 18 to 59 cm by 2100 - that is a really large range but even that did not satisfy the groups who felt it should be higher. Former U.S. Vice- President Al Gore’s 2006 documentary "An Inconvenient Truth" said we had 10 years to change things or a sea-level rise of up to 20 feet would be caused by melting of either West Antarctica or Greenland "in the near future". 2 feet in 100 years a year after science media printed 20 feet 'real soon' as fact annoyed a lot of people who wanted policy action on emissions.
7 inches by 2100 is not all that scary, even 2 feet is not worrisome. Sea levels change a lot. During the prolonged global warm period prior to the one we are in now, about 125,000 years ago, sea levels were about 18 feet higher than they are now, while during the last Ice Age they were so low people walked across the Bering Strait.
Ice2Sea has done what they call the most thorough assessment to-date and their figures are in range with the IPCC - ice sheets will add 3.5 to 36.8 cm to sea levels by 2100 and sea levels will rise by 16 to 69 cm.
As Michael Marshall and Andy Coghlan writing in New Scientist note, the IPCC was criticized for being too conservative because they lacked good data and models for the Greenland and Antarctic ice sheets and therefore they left it out. Other groups didn't like it and created more aggressive melting models. Yes, the IPCC was criticized by people who accept climate change for being too scientific. Ice2Sea says they have the models now and the IPCC is correct.
The IPCC is going to use this data in their 2013 assessment and that's important, assuming the numbers hold up. They need to be regarded as less of a political body and more of a scientific one and that means sometimes listening to or ignoring detractors about some models and conclusions - depending on the validity. Peer review works in science because if a peer asks the awkward questions, a scientist has to be able to either make a better case or realize they have more work to do. Picking a position and then science-ing it up is fine for politically-motivated publications or policy makers in the White House but it does not belong in the IPCC, which the public needs to regard as culturally agnostic and a trusted guide for a complex issue.
So maybe the IPCC was "hopelessly optimistic" in 2007, as detractors claimed - what is important for the future of climate science is that they were right.