First off, the majority of soakers (stock,modded, and homemade) are NOT dangerous.
That said, there are inherent dangers in using anything (heck, even walking can pose certain dangers, too), but acknowledging where potential dangers lie is never meant to suggest that something should not be used. Pointing out areas of risk are done simply to help protect the user from potentially injuring himself/herself, others, or causing damage to the soaker or other items. When driving a car, one has the ability to kill a number of people or even oneself if one is careless; thus rules and warnings and training are given to drivers to help them avoid such situations or causing harm. With soakers, the ability to kill another is extremely unlikely, but varying types of injury can be more likely depending on what is being done.
Dropping a heavy soaker on one's foot can be painful. Getting smacked at close range from a strong water stream can cause blurred vision for awhile. In the vast majority of cases, such injuries are only temporary and reversible, but as an advocate of safe, fun water warfare, I'd rather point out things that can be done to minimize risk.
Of course, in the end, safe soaker use is up to the individual. No number of rules can prevent accidents if users are careless. Some may also find some of the rules suggested too strict and are willing to relax some rules to facilitate gameplay. This, too, is fine so long as those involved are aware of the minimal, but present increased risks involved.
For example, use of non-filtered creek/river/lake water in a soaker will not severely damage a soaker or another (unless, of course, the water is extemely silty/muddy and clogs up the inner screens). Particles in the water, though, can be small enough to get through the mesh on a soaker (assuming the mesh is still there), adding a mini-projectile to the water stream. In most cases, this, too, is fine, but should the stream or splash get in another's eye, silt/sand is very unpleasant and would require proper flushing with clean water to prevent scraping of the eye's lens. The risk involved is rather small, but is still much greater than had the water being used be clear and filtered. Clean, filtered water does not absolutely guarantee that the waterstream is free from particles (things can still fall into the soaker reservoir or end up on the nozzle prior to firing), but the risk of getting something other than water into another's eye is dramatically reduced.
Another common concern is about how homemade waterblaster safety is presented. A well-built homemade is as safe if not even safer in many aspects than a mass-produced stock soaker. Construction-quality aside, the main differences between stock and homemade soakers is the potential power of the streams being unleashed. If a homemade soaker simply outputs a similar stream to a stock soaker, the possible chance of causing injury with such a stream is equal between a homemade and a stock soaker. However, as stream power increases, so does the chance of injury. Thing is, I know of at least two people who have been hit in the face/eye region (eyes were closed) from a decent distance (~15') by a CPS2000 Mk.1 stream and complained of blurred vision and discomfort afterwards. The ones hit were not the type to just complain for the sake of complaining and enjoyed using a good soaker, but they were shocked and sincere about their vision concerns. While no permanent damage was done, it did make our group adjust rules about headshots with larger soakers. As some homemade soakers are well capable of doubling, tripling, or more the output of a CPS2000 Mk.1, such soakers have the ability to do more damage if used irresponsibly. This is not to say such soakers shouldn't be used or shouldn't be pushed further; it's simply a fact about the dangers of increased waterstream power and a reminder for creators and users of such devices to respect their creation's power.
In the end, it boils down to the responsibility of the user who will determine whether a soaker is used safely or dangerously. Some seem to feel that safety is taken too seriously or dangers are over-emphasized. However, as these boards are open to a wide audience, as a promoter of water warfare, I feel it only proper to point out areas of risk to help those unfamiliar understand where risks lie. Water warfare is so much safer than the bulk of other war-type games out there, thus safety concerns should never be seen as discouraging others from participating or taking up the activity/sport. At the same time, I want water warriors to enjoy the full benefits of water warfare while minimizing the chance of hurting themselves or others through misunderstanding or lack of knowledge of potential risks.
Thoughts on the above or additional ideas/stories/etc concerning soaker use and soaker safety are most welcome.
In the end, it *IS* up to *YOU* to decide what is responsible water warfare for your group.
Addenum: I love water fights, but respect my soakers and the streams they output. IMO, knowledge of safety never detracts from a game, rather it helps ensure that all participants have a great time by avoiding unwanted accidents and/or injuries. There are, of course, some concerns over dangers that are too much and rather unlikely (or even impossible, depending on the misconception), but I'd never disrespect another with a valid safety concern. Caring about the well-being of all participants in a water war is never a bad thing.