I do not think it is really a matter of trust. If the DNS system is not being managed well, then it can be taken control of more easily than you might think. For instance, if the EU wanted to take 100% control of all of their TLDs and make them subordinate to a new root, it could be done. It would create issues temporarily, but nothing that could not be worked around. I think the issue with handing over control of the existing root and management of new TLDs is that it is hard to identify an organization and funding that would do a better job of competently managing the system, but there are certainly many organizations and countries that we don't want involved in managing the system. So the low risk approach is "If its not broke, don't fix it".