Should'a, could'a, would'a, didn't.
Yes I *SHOULD* do something... but that depends too. Is it that I SHOULD by my own belief? Because it's practical? Because it will benefit people as a whole? Because it will make my life easier? Because it'll help someone else?
There's so many factors to 'should', at which point is it "yeu should do this because it is the law, even if the law is pointless and goes against everyone's interests"?
There's other problems as well, how about "yeu should do this because it will benefit me but harm yeu", or "I should do this because it will benefit myself but noone else".
Should is really just an extension of value; value can be personal, it can be societal, it could be religious, it could be law. To each of these things, however, it is only an extension of value, and value is not a set in stone concept, but rather a perception, something which can be viewed at many angles.
Let's say yeu have a no win situation... yeu have 100 children held hostage. One of them is yeur own child. If yeu sacrifice yeur one child, the other 99 will go free. If yeu don't, then yeu keep yeur one child that is yeur own, and the other 99 perish. Whot "should" yeu do?
The definition of the term 'should' becomes highly subjective, there's so many factors in play, and the value of each one depends entirely upon yeur personal beliefs. No matter whot yeu do, there is no 'real' right answer to this question, as yeu're going to feel guilty no matter whot yeu do. Yeu will ALWAYS think after the fact "I should have done..." regardless of the decision made.
That being said, is 'should' as a word useful? When used to yeur own personal sense of value, yes. When trying to impose yeur personal values upon another? No. Because it is an extension of perception and will never properly apply to any perception other than the one it was born from.
As long as yeu maintain its' usage to its' own perception, it works well. "If yeu value life, yeu SHOULD do this". Tying it directly to the perception it correlates to will explain the reasoning behind it.
Just saying "yeu should do this" means nothing, other than stating "my values are these".
To use it as a statement of fact, without explaining the perception it's tied to, is to misuse the word. "Yeu should do this because to do otherwise is evil" means NOTHING other than stating "I value X", and it does literally absolutely nothing past that point. The only thing saying 'should' in that context did was specify the perception of the one making the statement.
That being said, should, as a word, is not inherantly bad. It's just generally misused and attempted to be forced as an absolute value, rather than a variable based on perspective and context.