You say that but ISIS have set up websites with instructions for evading these blanket collection tactics. They even offer software to do it for download. If data collection actually worked well then these people who committed the France atrocities would have been picked up before they did it.
Murderers you are correct not always the brightest person but you don't have to be bright to avoid leaving DNA/Fingerprints. Someone of average intelligence can work out that wearing gloves prevent leaving fingerprints. DNA isn't just falling off us constantly. Wearing gloves and not leaving any bodily fluids at the crime scene isn't exactly rocket science and would certainly make a huge database worthless. If the victim scratches you then ok a database would be worthwhile.
I can't actually find stats but I believe a fairly low amount of crimes are actually prosecuted based on fingerprints/DNA as there tends to be a much more obvious/cheaper link to make(I will try and find stats remember reading some a while ago). If anything knowing everyone's DNA/fingerprints is on record may actually make people more careful and thus harder to catch.
Again the Gun analogy doesn't work because one is removing the implement of crime whereas collection of data/biometrics doesn't.
If you look across the world and who commits majority of crimes, they would be hopeless in hiding their DNA + Fingerprints. Most of crime is not finely planned and detailed, they have an idea but execution of it is extremely sloppy.
I believe that having everyone's DNA in a database is more likely to serve much more as a deterrent rather than cause people to be "too careful" To not leave any DNA or Fingerprints on crime scene, you'd literally have to be in full bio warfare costume... Which would raise few eye-brows to begin with.... In the end a criminal would have to take a lot more steps in order to conceal and that increases chances of a slip up that would lead to them being found... Not necessarily from DNA but once they pull up that you ordered a hazmat suit from Amazon... then you know.
I do not agree with you that gun analogy doesn't work, people naturally weigh pro's and con's of their actions... You're more likely to agree to shoot someone rather than kill them with your bare fists... Since that carries much more risks and its not as easy. DNA + Fingerprinting would be a massive addition in deterring individuals from committing crime as they would assume that the risk is not worth it.
Heck, you give majority of US shooters a knife and tell them to stab their victim instead and they won't do it. Even if they did, the investigators would have a lot more to go on, since it would be a close contact that would give a lot more leads.
Combine it all into one system, where having a gun is red flag, ordering anything that is designed to hide DNA + Fingerprints is red flag, researching into "perfect murder" is red flag and then having your biometrics in the government database to top it all off, you barely have any chance of committing any murder. Even if you tried, you'd have to take so many steps that chances that you will trip somewhere along the chain-link is extremely high.
