The only ones I hear complaining about useless people are the conservative capitalists saying people need to work hard and not leech off benefits and welfare. It's on the other side, brother.
I agree that it is a common worldview I find among some pro-capitalists here, who seem to view people who get state support after losing their jobs as lazy/useless parasites.
But at the same time, people who earn millions or billions from sitting and doing nothing but manipulate money or create stock buy-/sell algorithms or spambot programs, or even the legal advertising of which the vast majority is nothing but propaganda that only serves to inflate our consumption of resources, or consider the people who get rich from paying the 25 million coffee farmers in the developing countries tiny wages and then adding several times the production costs to the values they're sold for in the industrialized countries, or consider all the people who work to produce wine, beer and all the other alcohol products, all the candy that contributes to people getting poor health, inflating the resources needed to be spent on healthcare and reducing people's productivity, those who work to produce cigarettes and those who make money from spreading this cancerous plague across the world, and so on. To me it seems like society would be better off without them in their current positions. Some of them are immoral parasites who are simply happy to see millions of coins pour in in proportion to the number of people who get cancer or COPD from smoking. The majority is obviously people who simply have jobs that contribute to the economy in the ridiculous system of capitalism, but who I would never blame for the faults of the economic system or the industry they work for.
That's not to say they're useless, they're not "useless" people, many of their current positions are, but of course they can get new positions that contribute to society. And people who can't contribute to society as in working (I guess that would be the "definition" of "useless" in this context if anything, not that people who can't work can't contribute in other ways to make all people's lives happier or experience good things themselves), I would fully be for them being treated just as well as everybody else if they are not to blame for not being able to work. On the other hand, it seems like some pro-capitalists think those people deserve to starve to death (the logical implication of a system with no guaranteed support for people who for example were born with conditions that would make them unable to earn money and thus support themselves), while it's fair that the money-manipulators can have incomes that are hundreds or thousands of times bigger than the people who construct buildings or harvest oats, or millions if they happen to harvest coffee beans.
In reply to the OP, of course we could put life on another planet and let it evolve, but I don't think it would be that interesting. You might as well create a small, special environment for the life forms you want to see evolve here on Earth, that would be much easier and cheaper to control and observe, and could probably be made very similar to the environment on other planets except for gravitational acceleration.
Finding life elsewhere in the universe would be a completely different accomplishment. First of all we wouldn't have to wait the probably millions of years it would take for macroscopic life forms to evolve if we just put life on another planet (if it wouldn't simply die out), secondly we could learn a lot more about the possibilities for life forms to exist or the probabilities of it existing if we found it independently of life forms on Earth. Maybe life forms elsewhere would be very different (chemically) from how they are on Earth, in ways that we could not achieve if we started out with (for example) bacteria from Earth.
As for setting goals for humanity, I think one of the most important goals is how we can maximize the happiness and minimize the pain of life forms that can experience it. The society that would come closest to achieving this I see as the classless communist society, the goal for humanity's future, that could be achieved through socialism and progress in technology.
I think another goal is to get the best possible understanding of the universe, simply because it's very interesting, but also because it pays off in terms of technology that can improve our lives. That includes searching for life elsewhere - this mostly falls under the interesting part though.