Pessimism is the ultimate self-fulfilling prophecy. It deadens motivation and creates paralysis. Why bother fighting if the cause is already as good as lost? Perhaps for this reason, pessimism seems almost comforting to those who would not fight anyway because they are weak or tired or don't really care. For the rest of us, it's a debilitating infection we should avoid catching.
No problem in history was ever solved by sitting around moaning and fretting about how bad it was. No conflict was ever won by a side which had convinced itself that its opponents were unbeatable. No one ever improved his situation by putting all his energy into complaining at the expense of action. The very act of writing off your cause as doomed will, in fact, doom it.
If you strive for what you want, you still might not get it. If you don't strive for what you want, you definitely won't get it.