The permanent UN security council members will veto anything they don't like. I believe it would be better if everyone got into an international bloc base in a region they are in, and police themselves.
Firstly, that already exists to some extent. It's basically what things like the EU or NATO are.
In many regions, rivals are "internal" rather than "external". A regional body may not function, because a country is trying to escape the influence of neighbours, not be "policed" by them. This is particularly notable when one regional country is far more powerful than the others.
There can often be little logic for where one regional bloc ends and the next begins. This in practice means overlapping blocs. Egypt for instance might want to be part of both a "Middle East" bloc and an "Africa" bloc. Major global players like China and the USA want their fingers in everyone's pies anyway.
This being back to the original point, having a theoretical higher power which is placing itself as though it has the ability to intervene leads to the arguments that lesser powers should not therefore intervene - they represent a lower proportion of the globe, they should not have to shoulder such a burden when nobody else can be arsed, imperialism / colonialism etc. The relative reluctance of the UN to do things despite positioning itself as the authority to do so, for better or worse reduces any chance of intervention.
The UN does not have authority in the way you suggest.
It has always been the case that powerful nations have dominated others. Many of ancient Rome's neighbours would not act without Roman permission. Many 19th century countries would not act with British permission, and so on. To a large extent, that is still the base model today. After all, no hugely powerful country is simply going to give up its power wholesale. The UN is designed with that underlying reality in mind.
In the old days, the only thing that determined whether a great power would do something was the whim of that great power; the old hegemonies were essentially tyrannical and represented nothing but the interest of the great powers. This could be catastrophic when great powers made mistakes, especially regarding the intentions of other great powers.
The UN is, if you like, an "advisory" board. What it does is to provide endorsement of certain actions. Under the UN, there has been an attempt to constrain certain activities to those which are broadly supported by many other countries. This is what the basic votes are about: what is the global consensus about right and wrong? After all, the more that's what is done is thought the right thing to do by as many as possible, the less likely it is to generate friction and conflict in the long run.
Obviously, the intent of the UN to a great extent was to stop great powers fighting each other, because that's what the world wars were about and everyone wanted to avoid, more so than two small and weak nations butting heads. That's what the vetoes are really about: great powers telling each other not to overstep certain red lines, in order to avoid cack-handed misadventures that might dump us in WW3.
Viewed in this frame, the UN is what it is and does a reasonable job of it, I think. It's not there to do what the USA wants because the USA pays more than any other country to its budget. It's not there to give orders and destroy national sovereignty. It's about letting every country know, formally, what every other country thinks about what they do.
Small nations can intervene under UN auspices if they want. The issue is that most can't, because they lack the military numbers, equipment, training, logistics or money to do the job on their own. The UN can maybe help them out with the money, and/or mediate an alliance to spread the burden across enough countries to do the job.