But that's thing with a moral hazard -- just look at banking and securities. If you jack around the majority of your customers, it will become public and cause a shitstorm, but it doesn't make the moral hazard go away nor has it prevented all manner of moral hazards in banking from being exploited.
And not every -- or any -- potentially "lost" video is going to be tied to some high profile incident where some innocent black woman in a wheel chair took a dozen rounds of 00-buck to her face. The most likely ones will be the low profile ones nobody cares about, where some obvious drunk got manhandled after bar closing and a dozen citizen eyewitness statements back the police version of events completely.
And it's also not likely that Taser would just delete videos themselves -- that's too obvious. Rather than running a system that's totally secure from police tampering, the inclination will be to provide a "friendly" system that offers soft points where the police can prevent videos from getting uploaded at all under the guise of technical glitch or something.