Well it isn't as black and white as you're painting it. It is correct that sometimes law enforcement are obliged to enforce laws they as a group or as individuals do not agree with. On the other hand law enforcement are not obliged to enforce all laws all the time at any cost.
The legal principle of proportionality states that law enforcement always have to consider whether their actions are reasonable in comparison to the violation of laws.
There is also a general concept related to proportionality that basically states that law enforcement actions must be strictly necessary or required in the given situation. Especially when the means of enforcement includes physical violence.
The legal principle of proportionality states that law enforcement always have to consider whether their actions are reasonable in comparison to the violation of laws.
https://en.wikipedia.org/wiki/Proportionality_(law)
There is also a general concept related to proportionality that basically states that law enforcement actions must be strictly necessary or required in the given situation. Especially when the means of enforcement includes physical violence.
http://www.ohchr.org/EN/ProfessionalInterest/Pages/UseOfForc...