While I agree that it's painful seeing evidence thrown out for procedural reasons, there is certainly logic behind it, as it provides a check on the power of the police. It may well be the lesser evil (as intended). Simply disciplining an officer who doesn't follow procedure may not be sufficient incentive to prevent people's rights from being ignored. That's especially true if officers cover for one another so it's not even possible to determine who is responsible. Unless the punishment is extremely harsh (which would unfairly penalize legitimate mistakes), it may often not be effective anyway, as many well-meaning officers could accept punishment in order to put (who they believe is) the bad guy away. The problem is, when you start going in that direction, innocent people's rights will be infringed as well. You already see cases all the time where innocent people go to jail due to police bending or breaking the rules. I have to think that allowing all factual evidence regardless of source would make that worse.

That said, it's obviously not a just result in an individual case like this. It would be nice to be able to have justice in these situations without losing the overall disincentive. I'm not sure that it's possible, but would love to be wrong.