[T]he absence of evidence is not the evidence of absence.--from a Heritage Foundation op-ed
Iran has a very open presence in Latin America. The question, then, is whether this constitutes a threat to the national security of the United States. Even the Heritage Foundation has to admit there is no evidence for that. But, it seems, we should proclaim it to be a threat even though we lack evidence.
The smartest policy position would be to stay aware of what Iran is doing, being careful not to lump every activity into the "threat" category and also being very careful not to confuse fact and rumor. Too many analyses of Iran (including the above op-ed) have too much of the latter.
Labeling something a threat prematurely is definitely a threat to U.S. security. The second Iraq War will always be a prime example of that.