'credibly argue' is correct and usable in written English.
It can be used to convey that someone has effectively argued a point. For example, "The lawyer was able to credibly argue his client's case before the court."
But can anyone credibly argue the tourism boycott has made it better either?
But at least nobody can credibly argue that baseball fans will not come to a Yankee Stadium in the Bronx.
This is because no one can credibly argue that Mr. Buck — or anyone else — should be capitally prosecuted, sentenced to death or executed because of his race.
Otherwise, the defense could credibly argue that it was impossible to time the injury and assign blame to a specific caretaker.
The two countries cannot credibly argue for restraining the nuclear ambitions of Iran, North Korea and other wannabes unless they keep working to bring their own numbers down.
In Iowa, New Hampshire, and South Carolina, Trump's opponents could credibly argue that beating expectations, but not beating Trump, was a kind of victory.
James Gilligan, the American psychiatrist specializing in violence, credibly argues that most personal violence is a response to such feelings of shame and humiliation, and the violent act is a horrendous way of equalling the score.
It can be credibly argued that at its creation NATO's mission was essentially defensive.
It cannot be credibly argued that this is the not the case, only that it is somehow worth it.
Furthermore, it can be credibly argued that the College is a knowledge-based institution that is too specialized to be entirely led and managed by non-health professional academicians.
It can credibly be argued that the health care bill will not make much difference one way or the other to the campaign.
