Programmers.SE has had a bit of history to it. Much of it you can read about in the Meta here and on Meta.StackOverflow too.
The short version (glossing over much) is that it started out with a very permissive "what is allowed". There were difficulties with this and a new direction was charted to something that is likely more in line with what exists now.
Part of that readjustment of vision has been a more active moderation (not necessarily moderation by moderators, but rather the community that has formed since). Part of this moderation is close votes, but part of it is also down votes - both are necessary as close votes don't always signal to the OP that the question is need in revision or fixing.
For some reason, there are many people who ask questions that aren't good questions for the Q&A format. Polls, recommendations, fix my code because I'm question banned at StackOverflow, etc... Without down votes, there is no way to signal to the person that they need to fix their questions. Whats more, down votes contribute to the algorithm that feeds the automatic question ban and stops people from asking questions that doesn't generate good content for the site.
I would suggest reading Yannis's answer in How can I encourage Stack Overflow to rein in the 'subjective' vigilantes?Yannis's answer in How can I encourage Stack Overflow to rein in the 'subjective' vigilantes? which goes a bit of the history with the stats.
Another bit to read is Optimizing For Pearls, Not Sand
Its not negativity, it is a firm commitment to keeping the quality of the site - the questions and answers you read and others come here to read - high. It is through this commitment that the site continues to grow.