alt Hacker News> pretty sure this is stems from the insane US legal requirement to not export SSL technology to enemy countries
This is most likely OFAC. Lets Encrypt could apply for a license to do business with sanctioned entities, and given their use case it would most likely be approved.
OFAC regulates commerce, not speech. Let's Encrypt is not doing "business", they're operating a free informational service. Lots of organizations interpret any information exchange as subject to OFAC regulation, and you and Let's Encrypt have good company in this interpretation, but I think it's unnecessarily ceding ground.