In our experience, counter arguments tend to come under three headings: (a) those based on misinterpreting the concept (b) valid problems that could occur and must be protected against in the legislation (c) risks that will never go away and have to be acknowledged.
Problems to be tackled
Beyond any misunderstandings, some valid concerns about NEMs should be addressed in the legislation:

Despite these points, it’s important to recognise there will be losers in a NEMs launch. The stagecoach business never recovered from the Railway Acts in the UK. Early airlines lost out when Air Traffic Control became a regulated level-playing-field equally open to newcomers. But NEMs won’t happen overnight. Its impact will become clear progressively and it will create new opportunities for those who are flexible enough to seize a space in the new landscape that we can’t fully predict at the moment.
National rail networks in the UK created the holiday industry, a far bigger sector than stage coaching. Federal ATC increased public confidence in air travel. NEMs will spawn all sorts of new activity; and make it very low risk to try new endeavours.
The unavoidable risks
The Times. 15th July 2008
We have to accept that yes, NEMs could go disastrously wrong at a point when potentially millions of people depend on it. An outage or Denial of Service attack on a system relied on by a huge percentage of the population would have catastrophic economic impact. But all centralised infrastructure carries this risk.
NEMs is a lot less sensitive than other infrastructure. Being deprived of the e-markets you took for granted would be inconvenient. But losing your water supply is devastating. It happens periodically on a small scale. It could one day happen across a whole urban area. There is no back up to the one public water supply. Yet we all accept that risk every day. We will have to do the same with NEMs.