The problem there is the slippery slope. Once a person has employed underhand tactics and been successful will they be able to use it with pure beneficence. There judgement might start off discerning but end as an post hoc rationalisation for what ever ends they figure is worth taking. The point is with morals it's always best when it has a firm rational structure that can be employed by the masses and externally justified as we are not always the best judges of our actions and motives. If you can decide to bend the rules why can't I?

Many philosophers have debated that concept for centuries.
Consequentialism, deontology, moral relativism, situational ethics, etc, etc.
I don't think there is a black or white answer.
Sometimes, the ends DO justify the means. Sometimes, they don't.
I'd just as soon make my decisions on a case by case basis.

There may be certain circumstances, where life is at stake, in such a situation someone may do something that would usually be deemed immoral or illegal. Lying to the eletorate to get elected to public office is not quite the same thing, is it?
You might want to consider "Prisoner's Dilemma"

Two members of a criminal gang are arrested and imprisoned. Each prisoner is in solitary confinement with no means of communicating with the other. The prosecutors lack sufficient evidence to convict the pair on the principal charge. They hope to get both sentenced to a year in prison on a lesser charge. Simultaneously, the prosecutors offer each prisoner a bargain. Each prisoner is given the opportunity either to: betray the other by testifying that the other committed the crime, or to cooperate with the other by remaining silent. The offer is:

If A and B each betray the other, each of them serves 2 years in prison
If A betrays B but B remains silent, A will be set free and B will serve 3 years in prison (and vice versa)
If A and B both remain silent, both of them will only serve 1 year in prison (on the lesser charge)

It goes I think by a case by case basis. If the ends are worse than the means then no. I would consider that Machiavellian. But if a politician tells a few white lies to get into power and then uses that power to legitimately make things much better, I can forgive them.

Circumstantial. I'd say if the overall goal is much better than the way of getting there, then it can be justified. But personally I'd probably try not being deceptive as a first resort. Just not that kind of person.

Islamic doctrine encourages it ”TAQIYYA”. That’s why we should totally buy the line that Islam is a religion of peace and Iran has no plans to develop their Armageddon weapon. Their nuke capabilities are only for peaceful purposes.

Never. Of times it is just an excuse to impose one's values /beliefs on another.

You would have to qualify that statement due to the actual circumstances and that usually isn't clear. Why is the way you see it right or wrong and why do you know best?

Current bad behavior for the promise of some future good result sound problematic on its face and I believe should be avoided.