No security system is perfect. The systems that exist in both the US and UK are considerably less than perfect! I too would like to see improved training for security staff, better intelligence, better flight deck security, and more passenger profiling (my airline is one of those that trialled it in UK, I believe). However, those things haven't happened and aren't likely to. Even if they did, I would still have no intrinsic objection to armed security personnel on aircraft - whether or not they could save any or every potential disaster is irrelevent. They provide one more layer of defence and deterrence at a time when we need everything we can get.
The practical applications of 'skymarshals', and their tactics and weaponry are irrelevent in this forum. They have been imposed by the UK Government, at the demand of the US Government (which is probably what's getting up most Brits' noses), and therefore we have to learn to live with them.
Skymarshals have been flying for years. I know of no security situation that's been made worse by them, and there are quite a few that have been resolved successfully by them.
There are more important things to argue about.
