>In fact, why would anyone bother putting their time and energy into "benefiting mankind" when someone else could do it for profit?

Well, that's precisely the problem. There's little space for people to do good in when success is based on capital accumulation.

>Automating farming away has taken away most of the farming jobs and that as a result has freed people to do something else like work in factories and produce things that didn't exist before

I think this is missing the point. The rate at which "new things" (requiring new jobs) are being created is, I believe, less than the rate at which people are born. People shouldn't have to work in factories, at least not at the amounts currently "required" today, and the only reason why they are working in such jobs is due to overproduction, less incentive to automate, and the contradiction which I mentioned in which capitalism requires a less than maximum standard of automation to function.

>I think we are incapable of imagining what we will accomplish when we are free of all the menial jobs that takes people's time today.

Are we also incapable of imagining what can be accomplished when people are free of jobs, or at least, the requirement to sell labour-power for wage? Labour-saving devices are being invented in nearly every field, and yet people are still having to work at the same rate. The rate of creation of fields without labour-saving devices (which thusly require large number of labour hours) is I believe reducing.

I see five reasons why people work so much:

1. Lack of labour saving devices in a particular field

2. Overproduction as part of the cycle of capital crisis

3. The more hours applied, the larger the amount of money the worker earns, and few hours are not enough to sustain one person or his family

4. Labourers need to buy back the products they create and they can only do this with wage and further with some "disposable" wage

5. The prevalence of government-run programmes encouraging employment rather than programmes which guarantee the ability of those with hard to sell labour-power to live without selling their labour-power (think pensions, but not just for those over the age of retirement.)

Of those reasons, you've only countered reason (1) with the reasoning that there will always be some area with few labour saving devices. I think this is a bit of a kludge (sort of like UBI in my opinion) and not something I would be willing to bank on given the rate of innovation. The problem lies in the dichotomy presented to us by our mode of production which roughly says: sell your labour-power, or live in poverty. This is alleviated (though not solved) only by government spending. I'll quote Oscar Wilde:

At present, in consequence of the existence of private property, a great many people are enabled to develop a certain very limited amount of Individualism. They are either under no necessity to work for their living, or are enabled to choose the sphere of activity that is really congenial to them, and gives them pleasure. These are the poets, the philosophers, the men of science, the men of culture – in a word, the real men, the men who have realised themselves, and in whom all Humanity gains a partial realisation. Upon the other hand, there are a great many people who, having no private property of their own, and being always on the brink of sheer starvation, are compelled to do the work of beasts of burden, to do work that is quite uncongenial to them, and to which they are forced by the peremptory, unreasonable, degrading Tyranny of want. These are the poor, and amongst them there is no grace of manner, or charm of speech, or civilisation, or culture, or refinement in pleasures, or joy of life. From their collective force Humanity gains much in material prosperity. But it is only the material result that it gains, and the man who is poor is in himself absolutely of no importance. He is merely the infinitesimal atom of a force that, so far from regarding him, crushes him: indeed, prefers him crushed, as in that case he is far more obedient.