1. The DNA is not collected for all arrests, only arrests where probable cause exists that the arrestee has committed a serious crime. Those are defined as murder, rape, assault, burglary, and the like.
The gov't/LE wouldn't expand that criteria later. They've never done anything like that before. (sarcasm)
2. The DNA will not be collected until after arraignment, at which point the reasonableness of the probable cause for the arrest will be determined by a judge. In essence, the judge will be determining whether things proceed to the next step, which would include DNA collection.
I think the "when" in regards to collection will be downplayed and ignored if they have permission to do so without a warrant. As is, Maryland collects DNA upon booking, not arraignment.
3. If the arrest does not result in a conviction that stands up to appeal, the DNA sample is destroyed.
It happened. Wiki: "FBI agents cannot legally store DNA of a person who was not convicted of a crime. DNA collected from a suspect who was not later convicted must be disposed of and not entered into the database. In 1998 a man residing in the UK was arrested on accusation of burglary. His DNA was taken and tested, and he was later released. Nine months later, this man’s DNA was accidentally and illegally entered in the DNA database. New DNA is automatically compared to the DNA found at cold cases, and in this case, this man was found to be a match to DNA found at a rape and assault case one year earlier. The government then prosecuted him for these crimes. During the trial the DNA match was requested to be removed from the evidence because it had been illegally entered into the database. The request was facilitated. [11]"
DNA collection I'm ok with if it has a reason behind it and has a defined place. Allowing it to happen during booking shouldn't be allowed. Fingerprints and photos are an identification. DNA is me, literally. Allowing the DNA collection to take place in order to perform a fishing expedition is just wrong. We already have emails, texts, phone calls monitored at any given time with just the slightest of pixie-dust evidence. All for fishing expeditions.
The other issue I have is the creation and maintenance of a DNA database. Who knows what will be discovered in the future that will enable the DNA database to be utilized in less-than-humane methods? Profiling, cleansing, enhancement, etc. Technology, throughout time, has broken through barriers painfully and harshly. The Wright brothers sparked technology that has killed tens of thousands. It enabled the greatest mass-murder in American history (all's fair in love and war). Technology is great, don't get me wrong. But when it's twisted in the control of gov't, good things rarely happen.