A) They might do something statistically invalid like charging whoever matches, even if somebody is bound to match just by chance. That didn't happen here. Usry was only a suspect and interrogated then let go. If he did get wrongly convicted, that means there's always at high risk of that for any investigation even without DNA. If we don't trust our processes for protecting against wrongful convictions, then we should try to fix those because they'll already be being abused. If we don't want police to interrogate any suspects who aren't already known to be guilty, then we might find they become a lot less effective at solving crimes.
"... was interrogated for six hours and finally gave blood for a DNA sample. For the next month, he remained under suspicion until his DNA was determined not to match the samples taken from the crime scene."
That looks like a perfectly normal and acceptable way of investigating a crime. It looks like the system working safely.
B) Police accessing personal data is wrong. How about phone tapping with a warrant? How about searching a house with a warrant? Private surveillance footage? Where do you draw the line and not allow them to investigate crimes?
C) People confuse it with secret anti-terrorist or antidisestablishmentarian (I found a use for that word!) NSA investigations which don't follow the well accepted warrant process.
D) Other.