It depends on what the expectation is. People can't/shouldn't just sit back, do nothing, and start expecting all kinds of things to happen for them that will make them feel like they're (as you implied, I think) getting something from life.
There is, however, a type of expectation that is reasonable and realistic. For example, expecting reasonable justice from a System that calls itself, "Justice system" is one. Expecting people to do their jobs with a level of conscientiousness and integrity and trust is another one. Expecting respect as a person from others, particularly when one respects other people is another one. Expecting people like parents to protect children or people like those in "The System" who are supposed to protect children, elderly people, and/or other victims/potential victims to do that isn't expecting too much.
Neither is expecting too much in a country that claims that people have rights it unreasonable to expect that those rights mean something (and if they're ignored then the person/people involved shouldn't be expected to just sit back and say, "Oh, well...".
These are just a few of the "zillions" of expectations that people not only SHOULD have but should not allow anyone else to tell they shouldn't have them, or that they have no right to them.
Reasonable and realistic expectations should not be confused with "plain old hope" (which can be at sometimes realistic enough but which may not turn out well; also, there can at times be the kind of hope that people have when they're well aware that things won't work out but when they choose to err on the side of hope as long as a shred of it remains).
Hope is not necessarily "magical thinking", as someone has suggested. And, the fair and reasonable and realistic expectations of someone who has done everything he could possibly to do to assure that he has (and has earned) so many things that help that person feel as if he is getting all kinds of things out of life (and by "things" I don't mean "stuff"/"material belongings, although they're sometimes part of it) is something that person SHOULD have and should never be talked out of.
There may be two kinds of people who think you should not have reasonable expectations: The kind who passively, weakly, and hopelessly sit back and say, "Oh, well..."; and the kind who would NEVER do that but who think that YOU should. The ones who think you should are often the same ones who have failed you and/or failed to do their job.