Perspective
I think people need to get some perspective here. Whilst there may be some bad policemen (there are in any profession), the vast majority are actually good and operating under extreme pressure. Society is becoming more violent, their hands are becoming more tied and they are attacked within the press etc. at every opportunity. Politicians tinker around with laws all the time introducing loads more to understand and enforce, the current vogue being making them so vague, interpretation and a certain amount of miss-use is inevitable.
As for the mistakes. Whilst accepting that the result was in error, it is not this that defines the actions as good or bad, but the circumstances etc. leading to it and what people believed. In the Stockwell Tube shotting, the officers on the ground were told that the man was definately the bomber. They were led to believe he probably had the bomb on and was on the way to using it. Therefore, when asked to stop him, they believed they were dealing with a man wearing a bomb vest, very willing to use it etc. Common sense would probably tell people to run in the opposite direction, but they ran towards him and used lethal force to prevent the detonation of the bomb they believed him to be carrying. The number of rounds fired is irrelevant. You use as many as is necessary to ensure the person can't detonate the bomb and then add a few for safety. So, the issue here is not the people pulling the trigger, but the whole inept chain of command that ran the operation so ineptly that the people on the ground were lef to believe a complete fantasy. In reality, he had not been positively identified etc.etc. So, don't blame the shooters, but the senior commanders etc.
The same can be said of many of the other instances. Circumstances can lead to life and dealth decisions being made in a split second, often with inadequate or wrong information available. Under these circumstances, mistakes will be made. It doesn't necessarily make the person pulling the trigger a bad person, simply someone that tried to make the best decision he could and got it wrong. The fact the result was in error doesn't necessarily mean the actions or events leading up to it were wrong. Also, people need to understand that being drunk and refusing to obey armed officers is simply not a good idea.
Armed officers are putting themselves in harms way under very restrictive rules of engagement. There are many components of the decision making process that are far from satisfactory in these circumstances. The extreme stress normally present at the time, the lack of information (sometimes), the testosterone and adrenalin surging through their bodies etc.etc. None of these are known as catalysts for good decisions, but they are normally present. It's very easy to judge in the cold light of day, or a comfortable courtroom, but much harder to do it for real. Erring on the side of caution is understandable.
The difference with the use of tasers is that often they are used when these factors are not present. The Canadian hospital patient is a good example. The circumstances were such that a sensible, considered decision should have been possible. Indeed, this is a very good reason why tasers are of limited operational relevance. According to the guidelines, tasers are only supposed to be used when the alternative is lethal force i.e. firearms. However, if you are in a situation when firearms are justified, you or someone else must be in immediate danger. In these circumstances, you'll probably want someone more reliable and certain than a taser e.g. a firearm. In circumstances when you have more time etc. to make a considered decision, tasers are not supposed to be used!!
So, what people are afraid of, and there's a lot of evidence to support it, is that tasers are being used outside the guidelines and when other methods would have been used in the past. Whether this is right or not should be a matter of a public debate, but the government are not good at this. They only talk to people who support their position!!
If you have to confront a knifeman, is a taser a suitable method of disarming him? Possibly. However, as has been shown by stories from around the world, rather than being a considered option, it is often the default assumption and therefore used when not appropriate. Again, the hospital patient in Canada is a good example. Additionally, if a non-ranged use occurs, this rather defies the purpose of a taser. The point of a taser (generally) is that you can disable a person without getting too close. So, if your within arms length (and a non-ranged use mandates this), you've already put yourself at risk!!