The first thing to know and understand about Stack Exchange:
We are the anti-forum.
In fact, we're basically anti-anything that doesn't produce good answers to your questions, and that includes social networking (although it could be argued that we're actually the most successful at this, because we don't put up with the crap that is generated by most social networking sites).
OK, now on to some of your specific points:
many of the questions posted all have really low reputations points
Most questions asked on Stack Overflow are pretty pedestrian, and don't really warrant any votes. "How do I fix this?" A lot of our members have motives that are more altruistic than reputation points (we like to help), so we help when we can, but many questions are "under-specified" ... There's insufficient information in the question to answer it.
We save our upvotes for interesting posts for the most part. It's an imperfect system, but it works.
The ability to delete down-voted posts, the ability to block users ( trolls, etc. ).
We do have that capability. Now for what you were really asking:
Why are there so many users with low “reputation” points?
Would it surprise you to know that the vast majority of visitors to Stack Overflow probably don't even have an account? The veteran users forget this sometimes (I know I do), but the audience for our website is not Jon Skeet or Eric Lippert; it is everyone on the internet who has an interest in programming.
Most visitors to Stack Overflow have one motivation only: they want to get an answer to their programming problem. To get that, they can either find an answer that's already there and leave, or they can create an account, ask their question, get an answer and leave. That's why you see so many 1 rep accounts. These folks don't care anything about reputation or badges, and that's perfectly fine.
This, incidentally, is why Stack Exchange can make money. We veterans never see advertising because we have enough reputation that ads are turned off for us, so we're baffled that Stack Exchange keeps hiring new people, but most users do see ads, and those ads can be specifically targeted to the site topic, whether it's bicycles or kosher meat.