I think there's a large difference between threatening arrest and threatening direct violence. For one thing, arrests ostensibly may lead to review and double-checking of the case with lawyers and judges and the chance to defend yourself. Mistaken or invalid arrests may be undone. Direct violence can not be reviewed and then taken back.
If someone threatens you with arrest, they are threatening to send a group of armed men to your house. If you don't let them in, they will break down your door. If you don't let them physically restrain you with handcuffs, they will grab you and perform pain compliance holds, pepper spray you, or tase you, then chain you up with handcuffs or other restraints. If you resist to the point where you threaten their life, they will shoot you. Then they will physically remove you from your home and put you in a cell. Is this not violence?
With this logic, there's no difference between "our cops will enforce speed limits by pulling people over or sending fines to later" and "our cops will immediately beat or shoot anyone on-sight that [the cops say] are breaking the speed limit".
In the first case, if I choose not to resist (which I definitely won't if I believe I'm in the right and I trust the review/court system), there's much less risk of direct bodily harm, permanent injury, or death, even if I get jailed. If violence happens during the arrest, presumably that will be considered unusual and the cops will be at risk of being in trouble from that, so they have an incentive to not be violent. In the first case, if I'm wrongfully accused, I get to have my day in court, have a professional represent me, and present my evidence to a judge before anything more irreversible happens to me than losing some time. In the second case, I have no recourse if a cop abuses their power because they're reckless or have it out for me specifically. In the second case, it's already established that direct violence is expected, and because it won't be seen as unusual, the cops have little need to restrain themselves.
