The issue is the weekend warriors who think this is all a jolly good game,
I know of quite a few Reservists who do the job as well as any Regular, and even relied heavily on them in my last unit because they weren't part of the head count and were cheaper.
However, there is always a nagging doubt that there are many many more who don't take things as seriously and do see it as a jolly good game. I know people swing the lead in the Regulars too, but you just have to look at the likes of RAF News and Soldier magazine to see Reservists going all over the world on AT, doing interesting exercises and generally having access to a far greater amount of carrot than the Regulars and a lot less stick.
I realise that to get people to give up their spare time you have to make it attractive, but to many Regulars who are constantly on the receiving end of stick and not much carrot, it smarts a little. And I suspect, from talking to numerous people, it is that discrepancy that is likely to be contributing towards at least some of the negative feelings towards the a Reserves.
The other key point that people would do well to remember is that the military is renowned for it's professionalism and can do attitude. Many individuals will have gone through years of tough training and accumulated significant experience. To be suddenly told by the politicians and senior officers, who have no understanding of what if actually takes to do your role to the standards expected operationally, that it is now going to be filled by the Reserves can't lead to anything but feelings of being undermined in a professional sense if the job is now capable of being done by "part-timers" with a fraction of the training and experience.