Respectfully...
Investing seems like it is fun and easy to a lot of people who haven't done it. I'm not saying it is or isn't, I'm only saying that there's a perception that it's a fun and easy job. That perception might be right or wrong, and might not be a simple binary yes/no.
Sure, there are big plusses, and yes you can make a lot of money doing it. Starting a company is no cakewalk either, and investing is a nice way to get paid while enjoying the ability to talk to lots of smart folks who educate you about a broad array of subjects.
It's also not easy. A lot of investment funds fail. Not everyone is enjoyable to deal with. There are many hard truths.
FWIW I know a VC who left investing to start another company b/c he hated having to say "no" to so many folks, and to deal with some of the other pressures in the environment. There are negatives that aren't always obvious. http://www.quora.com/Venture-Capital/What-is-the-worst-part-...
As to your bigger point about the moral and social value of investing -- I think nearly everyone would agree that religious and community leaders are more deserving of high praise than a VC. In some cases, people who sweep their sidewalks might be adding more social value than some investors ;)
That being said, I think it's unfair to paint every investor with the same brush.
A good VC adds value and helps companies grow and succeed. The jobs created are good for society. A company like Tesla also serves a bigger good -- moving us from fossil fuels to renewables is a good thing for society, and capitalism is an effective tool for pushing that forward. The people who gave Elon Musk money to make that happen are (indirectly) helping.
Not every company is quite so noble. There are certainly lots of terribly useless investments -- http://www.businessinsider.com/a-year-later-41-million-start...
That being said, if we're going to point the finger at the investors, what should we make of the business people and engineers who work on these 'useless' apps? Are they also profiting from socially useless activities? Is there no room in human life for entertainment? Is there no value in an app that makes it easy for families to share special moments with one another?
I think there's a certain amount of acceptance required that not everything in a society will/can be focused on directly moving that society forward in the most obvious way, and being ok with that.