The issue is that, objectively, you can't accept two radically different positions as both being true. While maximising security or freedom may be in the best interest of a society, the decision will still be opposed on moral grounds, whichever you pick. For instance, if we had armed police and cameras on every corner and it was an unquestionable truth that this stopped violence, we'd still decry it as an attack on freedom.
And further, moral positions aren't necessarily empirical. You're saying morality is objective because you can objectively decide what is "right" but what is "right" is inherently very subjective.
If it was somehow irrefutably proven that legalising pot would have disastrous socioeconomic consequences, a lot of people, including myself would still argue for legalisation based on the maxim "I'm a big boy, I can make my own decisions" which doesn't make much logical sense if it's proven in this hypothetical world that we can't make our own decisions, but is somehow appealing regardless. In other words, what is "right" can have nothing at all to do with the best outcome. In fact, in my example, the worst outcome is the one that is the most moral, in my eyes.
Here's another example: animals. Would you kill a human to save two cows? Doubtful. Would you kill a human to save a million cows? Still, probably not. But what's the reasoning behind that besides an unempirical moral hunch that a human is somehow worth a million times more than any other lifeform?
Yes, you can, if the outcome is the same. I only illustrated it that way to explain in a clearer way how they may not necessarily be in opposition. You are probably right though, a society where security is excessive will probably not have the best results, so a system that balances freedom and security would possibly be the best, although in principle, if we were able to fully trust the government somehow (if they wouldn't exploit people), such a system would work great. The same thing goes for a free society (an anarchist one if you like). Such a society would be the best for everyone if trust was possible among all people. As for your example in the secure society scenario, you have to acknowledge that the usefulness of such a system doesn't depend only on stopping violence. It also depends (like I said before) on being able to trust the government. Why do you think people are afraid of surveillance? Because they can't trust the government. If it was somehow proven that whoever was in charge of this type of surveillance can be fully trusted, then anyone who would object to it would simply be wrong. Their opinion wouldn't be fact-based. We often perceive threats where there are none, so we can be wrong about this stuff.
It's not subjective. The moment you accept that the worst possible misery for everyone is bad (and that there is nothing worse than that), then you inevitably have to accept that everything else is better, so there are right and wrong answers. If you think that well being is a term too loose to base an objective morality on (you are welcome to find another way to define morality), then think about the medicine analogy. What is medicine as a science all about? It's about health, and health is also something that we can't define clearly, something that is always changing (life expectancy has increased dramatically in the last few centuries, who knows how long we'll live in the future, we might even be able to regrow lost limbs, etc). This doesn't for a moment make people doubt that medicine is useful, that it is science and not just opinion (subjective).
Well, you're not up to the conversation in that situation then, if you argue that your freedom trumps the well being of others. It's not just about you, we're all in this together. Your opinion has to be based on facts to be (objectively) valid. If in this hypothetical world, legalizing marijuana would be detrimental to society, we would have to evaluate the risks. What makes it so dangerous? Is marijuana inherently harmful\toxic? If legalizing the sale of marijuana would make a big part of society irresponsible, if it would cause a societal decline, then the answer should be clear. It should be illegal. In this situation, arguing for the legalization of pot would be comparable to arguing for the legalization of cocaine. You could in theory do this drug (or any other truly dangerous drug) casually and still be a functioning human being, but it's not hard to imagine that legalizing it would be detrimental overall.
This hypothetical situation doesn't help much, because, well, it is pretty much inconceivable. The only thing that it illustrates is that it is possible to be wrong, to have a wrong "hunch". Why do we care more about hamsters than mice? Most of us have no trouble killing mice or even find them disgusting, and granted, mice are a sanitary problem and this gives us an excuse (not a justification) to kill them, but we could just as well dispose of them without killing them. We could in principle establish that the lives of a million cows are more important than one human life, but we need all the facts about the situation, we need to assess the suffering of the cows and compare it to the suffering of the man. If we knew for certain that those cows would suffer more, it would be perfectly clear to us that they should be spared. This is no different than the trolley problem. Whether we know the objective answer or not, the answer exists and it can be (in principle) found by science. We could examine the brains of the cows and find out how much they are suffering.