I oppose keeping the fingerprints of people who have been determined to be "innocent" whether the prosecutor is unable to convince the jury of guilt or the district attorney drops the charge altogether.
Keeping the fingerprints says "we may not have proven you were guilty but we still find you to be suspicious of other crimes, we may need these later..."
Why can't the information be held until the case is proven?
We don't want the government to keep data from the "background check" for firearm purchases.
So do career criminals, and they applaud your stand on their behalf.
How often does it happen that fingerprints taken in one case match those found in another? Rather frequently.
If someone is arrested and printed, and later released, their prints sit in a database and do nothing, unless those prints later match a crime scene. The world is imperfect, but that's a better one than you're proposing, which would leave many crimes unsolved and unprevented.