Is it normal for things to be so cutthroat, and what to do about it?
Reality is very complicated. It is not one way or the other, often a mixture, and lots of judicious decision-making is required. Some environments are nicer than other, some people more trustworthy than other. If atmosphere disturbs you, choose your environment and the people to suit your taste, there are more pleasant subfields than others. 

Careers do depend on individual success, so you cannot just plainly discount people trying to keep their ideas for themselves until they are ready to capitalise on that - success, as measured by hiring committees, is individual, not collective. 

Yes, a fully open community is a bit like communism - great if it works, but usually works only to a commune of a limited size, or if the work to be done cannot hope to progress more than differentially faster than the community as a whole  and also if there are no "bad apples" who do not play ball and prey on the goodwill of the group.

That being said, you can encounter very friendly communities, but if that is a priority for you, you need to include that into your criteria for choosing a research topic.