Indeed. But remedies exist. Statisticians can examine the validity of the data, analysts and detectives can be trained to interpret the results correctly, and social scientists can point out the dangers of relying solely on computer systems.
I have no strong view for or against breathalysers. I'll concede that there may be some errors in those tests. Does that completely invalidate these tools in judging if someone is too drunk to drive and may cause harm to self or others? Should we only opt for rigorous methods like drawing blood samples? My view is: no, we should not. These are valuable tools that work for the large majority of times and help save lives (at the inevitable cost of some errors and inconvenience).
In my world I believe in just intentions. Breathalysers are not introduced to imprison sober drivers, they are to combat drunk ("lazy, incompetent or malicious") drivers on our roads.
These methods are useful for catching the savvy criminals too. I am not ignoring that these systems are also useful to target activists and political dissidents. That's basically what they were build for in the first place (well, that and the terrorists, see DARPA LifeLog). It's just now that these tools are adopted by local Police departments.
A weapon stick can be used to subdue a suspect through non-lethal force, and it can be used to choke a peaceful protester. It will succeed in both tasks. It's not a stupid ineffective tool we should take away, because it can be used in bad ways. We should make sure to avoid the bad usage, and provide police with the best weapon stick possible for the good usage.
You assume that this system will be used to justify police brutality and that this system will be used by people who think that any black person is a "criminal". I have a higher opinion of the people who join the police. I rather reserve such judgment to the criminals themselves.