I think that it is the only major leading source from where we can actually earn bitcoin
but i am not sure about trading
Gambling is something to avoid , trading could definitely be profitable If you know what you are doing but before starting to earn , you will probably lose the time you start learning lessons about it. Basically , you can do whatever you do to earn fiat to earn BTC , offering services on the forums is probably the easiest thing to do at this point but require some skills (web/app development , design etc...)
Right. In any gambling scheme, odds are stacked firmly against user by the house. It just common sense, as the user is only source of income for gambling company. Not vice versa.
From purely pragmatic point of view, daytrading should be also discouraged as 80-85% daytraders ends up in loss. Chances that you or me are that special, yet "not insider" kind of snowlake are very low.
Campaigns are cool, especially considering, that a) You take zero risk to your own portfolio. b) Value of BTC goes up overtime. Another option is to provide some kind of service (translation, web programming etc.) and get paid in bitcoin. When active in campaigning you can make close to 1 BTC a year. Wont make you rich, but it is viable to having savings at your local bank.