Why do your PD friends care so much about protecting the rights of their "clearly guilty" clients? It's because protecting the guilty's rights ensures the innocent's rights are protected too.

The trope here is the suggestion that criminals are getting off on technicalities. As you've illustrated with Miranda, even with the improperly-obtained evidence suppressed, he was still convicted. The government doesn't need to violate people's rights to keep criminals off the streets. And perhaps there would be fewer of those pesky appeals if the state did things right the first time.

Of course most 4th amendment decisions concern guilty people - the remedy for 4th amendment violations is suppression, so you never hear about the innocent people who are harassed by police with illegal searches - no evidence is found so there's no case with evidence to suppress! (Civil action is an uphill battle even for those who are able to bring it.)