The part about the brake light doesn't sound like a good idea. Police do encounter people with more serious warrants while responding to minor infractions or calls. Some of these individuals are dangerous. It's best to have the equipment needed to deal with those situations. I think the shortfall is that some people lack the training to go with it.
are you saying police need to pull people over for minor infractions because a) this is a good way of catching people with serious warrants, or b) police need to pull over people for minor violations anyway and they need a gun in case the person turns out to be a violent criminal?
in the case of a), I think this is the kind of fishing expedition bs that makes it hard for people to trust the police. the idea that they are not just going to ticket you for the thing they actually saw you do, but also make the most of the opportunity to look for anything else you've done / are doing wrong seems needlessly antagonistic. I would also question how much more effective this is than compiling a list of the fugitive's vehicles, known associates' vehicles, stolen vehicles, etc. and just checking the license plate reader against it.
in the case of b), this is kinda my point. if there's a meaningful chance that the officer or the offender ends up dead in a traffic stop, this should probably increase the threshold for what kind of offense justifies a stop. a broken brake light isn't worth dying over for either party. just take a picture/video and send a ticket to the owner of the vehicle.
in the case of an officer responding to a call, they no longer have the initiative to decide whether an interaction needs to take place. in this case, I think it is much more justifiable for the officer to be armed.
There's always a chance that a person (including a cop) becomes violent. Do we just remove all laws? I don't think so. On a side note, there are plenty of laws which are already not enforced or not consistently applied and should be taken off the books.
the thing that strikes me as particularly tragic about these police shootings is how many of them started as confrontations over fairly minor offenses. would it be so bad to just let a few more people get away with petty crimes? or better yet, can't we find a way to hold these people accountable that doesn't involve a face-to-face encounter with an armed officer?
"gives legal grounds for a traffic stop but doesn't really justify it."
What do you consider justification? According to the law and police regulations, it would be justified. Logic also supports the idea that if there is a law on the books, it should either be enforced or removed. In this case the law has the purpose (as almost all traffic laws do) of promoting safety.
"circumvent the default protection against unreasonable search and seizure"
How so? As I stated before, the law's purpose is to promote safety. Also, when you sign your registration card or driver's license, you are agreeing to obey the traffic laws. This isn't just some made up excuse to violate people's rights.
"can't we find a way to hold these people accountable that doesn't involve a face-to-face encounter with an armed officer?"
We already do this for some infractions like red light cameras (what a disaster) and speed cameras. It's possible this could be expanded further, but probably wouldn't be able to fit all driving laws or areas. Also, what's wrong with the officer being armed? This shouldn't have any negative impact on the stop and should be reasonable since there is a likelihood that the person could be armed too, which most of the time is not also not a problem.
in general, I think there ought to be more parity between what cops are allowed to carry and do to defend themselves and what is available to civilians. if every patrol car needs an ar-15 in the trunk to safely traverse an area, shouldn't people who actually live there be allowed to at least carry a pistol? or alternatively, if it's not okay for a civilian to carry any sort of firearm, why should it be okay for police?