As a propaganda technique, outing has two distinct meanings:
1. Originally, it referred to attempts to shame opponents by revealing their associations with groups, actions or categories that the public disapproved of - homosexuality for instance, or membership in the Communist Party. McCarthyism was a trend towards this kind of identification and very often included claims that were simply not true, pure propaganda.
2. As public disapproval of the things that were traditionally useful to discredit someone for official posts waned, it became more and more common for officials in a position of power and privilege to reveal the names of lower level agents. In previous eras this would have opened them to be prosecuted for treason if they revealed the names of agents on active duty doing security work. This happened at least twice in 2003 in the cases of David Kelly (who killed himself) and Valerie Plame. In this form of outing, the allegations are probably true, the person is no longer effective as a trusted agent, some of their assets are lost to the state, and presumably more "politically reliable" agents take their place. There may be shame involved, but maybe not. It may be of an intense and personal kind - Kelly killed himself.
In both senses, the term outing implies that a selective exposure has been made. If a deliberate and fair-minded effort is being made to expose all people in a certain not-trustworthy category in positions of trust, or to reveal all people who had any contact with certain pieces of information, an outing is simply part of an inquiry. It's the selective nature of it that makes it useful to identify and eliminate possible political and ideological opponents from a power structure, and which makes it extra-judicial and not a part of ordinary oversight activities.
A smear is often portrayed as an attempt at outing, but generally describes a case where the allegations are not true, and not made against a large number of persons with some other affiliation not relevant to the smear itself. A smear is aimed at getting the public to vaguely mistrust someone, not at getting a particular person eliminated from the power structure by specific verifiable accusations as outing is.
Before the war on terrorism and weapons of mass destruction in Iraq. Dr David Kelly, a trusted member of the Iraq weapons of mass destruction investigation team. Leaked to the media that -there were no such weapons, and there was no such threat. It was all being spun by the government.- The security services and executive power in the UK then closed ranks after he was exposed to the media. They claimed that there was reasonable evidence for the war, (as of 2 years later, this has not materialised, both President G.W.Bush and former Prime Minister Blair have stated that apparently they don't exist). The courts became complicit when the Hutton report, damned the BBC for broadcasting the leak, which turned out to be a better representation of the facts than the whole government/security services line. The only important thing here was apparently that, as a government employee he should never have been giving his opinion to the public. That was treason under the official secrets act. As a result he lost his job and reputation for being correct, the government and Secret Intelligence Service (SIS) united in the fabrication of hearsay and imagination and left him out in the cold. He killed himself.