For starters being arrested for a crime felony or not you don’t forfeit your constitutional rights namely your fourth amendment rights.
On conviction of a felony you do lose constitutional rights but only on conviction. Not for an arrest. You have to show probable cause to seize anything. Some people may say what’s the big deal if you have done nothing wrong. Would you let them search your house simply because you got caught speeding?
This goes far beyond searching your house, they are taking a piece of you. While they always make promises that it will only be used for criminal investigations history shows that the government never keeps those promises. Putting your DNA in a database will eventually be used for other purposes. Obamacare is a classic example, your DNA can be used to determine what diseases you may be prone to, you could be denied government jobs because of this, it could be used under Obamacare to determine how much money they will spend on healthcare based on what diseases you are prone to. Demand probable cause before forfeiting your rights.
