>Alright, but they were probably acting on behalf of some rulers.

I know you said I can ignore this for now, but I might as well address it while I'm writing this comment. To think that someone made a breakthrough in the field of ethical philosophy at the whims of someone more powerful all for the ends of having people be okay with whatever leader is in power to do what he wants under the guise of Utilitarianism is far fetched. Not to mention, Utilitarianism didn't catch on for decades afterwards anyways. It's much more reasonable to think that they simply were philosophers who wanted to contribute to the field.

>I've heard another definition of Utilitarianism where the idea is that the morality of an action is determined by its consequences

You're right in that they are compatible. When people describe Utilitarianism as consequentialist it's more to highlight its difference from Deontology than to define it 100% accurately. Utilitarianism values happiness, and happiness is the result of actions. So they are compatible.

>A central problem with Utilitarianism is that people act based on their perceptions, but the perceptions themselves are based on any individual's sense data, thought-patterns, pre-conceived notions and so on, and thus, they are subjective.

What you're essentially saying is that we aren't perfect and we can never have all the data that is involved in a certain situation; and that's fine. Every moral system would suffer from this, even the "Non-Aggression Principle" which I'll get to later. Furthermore, it also seems that you're saying it's far to difficult to have all the information and to execute perfectly accordingly. To respond, first: something being difficult doesn't make it not true. Second: unintended consequences would be a problem in any ethical system, even in "intention based" ethics. No one can simply ignore results even if you choose to value intentions more.

>So if people are just going around pursuing "well-being", there's no telling what they might decide to do.... boils down to, is the idea that the end justifies the means.

This is similar to the issue you raised earlier in that we can't gather all information and that we can't always perform the right action since we're flawed creatures. I completely agree with you here. But again, the outcome of people trying to maximize the happiness of everyone else if better than any alternative I can think of. And yes, the ends to justify the means if the ends include making everyone happy.

>For example, I might decide that some exercise would be good for you, and chase you around with a baseball bat to enhance your physical well-being. I'd think that my end would justify my means, but you wouldn't consider that moral, would you?

It's interesting that you bring this up because John Stuart Mill address this point explicitly in the following book: On Liberty (great read, definitely pick it up!) Essentially he says that we should respect the liberty and autonomy of everyone because forcing someone to do some other action (even if its a better alternative to what they're doing) is ultimately worse for their well-being. Because that person will be happier with that lesser action that they're doing than if they were forced to do an action that, while is slightly better, is ultimately not what they want to do.

>Only an objective moral system is distinguishable from having no morals at all.

Utilitarianism is an objective moral system. Could you please clarify what you meant here?

>guided by our consciences

It's not outlandish to think that if we had 1 situation where we had to choose an action and there were two people present, that those two people can have their consciousness tell them to do opposite actions. That being granted, if you're saying that consciousness defines the good of an action, and we can safely grant that two people can have their conscious tell them two opposite actions are good, then that logically contradicts. You are essentially saying action A is good and action !A (not A) is also good. You can't have A = !A due to the law of noncontradiction.

> "The Non-Aggression Principle"

Intuitively I would agree that this is a good moral compass. However, you're freely asserting this as a moral truth without any backup. "What you freely assert I freely dismiss." Personally, I think that the right ethical system will boil down to "Do what makes you happy, while not harming others in the process" (with some exceptions), but getting there requires a lot of philosophy to be done first.

Sorry for the long post, but you brought up a lot of good points I wanted to expand on!