Iran's support for Hezbollah
Comparing Iran's support for Hezbollah - allegedly supporting terrorism - with US support for Israel, we see that the US does support terrorism far more explicitly than Iran. Israel is an occupier (West Bank, Gaza, Lebanon) denying self-determination and an aggressor (1956, 1967, 1978, 1982, 2006, 2008/9) and defies numerous UN resolutions (those vetoed by the US excluded).
Based on UN resolution 42/159, the accusation that Hezbollah is a terrorist organisation is void because "people under ... alien domination" have "an inalienable right to self-determination and independence", the resolution upholds "the legitimacy of their struggle" and confirms their right "to seek and receive support". Armed resistance against the occupier with help from Iran is therefore legal.