Is it necessarily lying?

If you go to a conference for a hobby that's tourism, right?

Very few people speak at conferences as a hobby. Even fewer speak at conferences as hobby about things they get paid for. Even fewer would be legitimately willing to do this if it included an expensive middle-of-the-night flight, jet lag, and a Visa application process.

I've done it. Of course, I didn't travel internationally just for the conference and I didn't need a visa, but I've attended tech conferences on my own--including speaking. Why not? And how many Europeans who attend FOSDEM or Americans who attend Flock (admittedly a lower bar than traveling internationally) are doing so on their own?

Generally, when you apply for a visa, there's documentation guiding you towards the correct type of visa based on purpose of visit. Everything I've seen buckets conferences under "business visa".

That changes the parameters of the hypothetical. Your original hypothetical was explicitly about misrepresenting the purpose of one's visit to a country, which one should not do because that's illegal. *OBVIOUSLY*.

Whether attending a conference for a hobby counts as a vacation trip or a business trip would be a question for the destination country's consular affairs office.

> If you go to a conference for a hobby that's tourism, right?

That's exactly what I was told (as a statement, not as a question) by an official a few years ago when applying for a visa for a trip to Germany.

I know governments aren't always commonsensical but it would seem odd if someone (not in the business) would need a business visa to attend Comic-Con or similar.

That would explain the "are you a terrorist?" forms I've heard they're asking people to fill in on their flights to the US.

That's actually precisely the reason. [1] It's not always easily possible to arrest somebody for having been or even being a terrorist abroad, but you can definitely arrest them for lying on their visa application papers.

[1]: Well, probably. The Department of Homeland Security doesn't give an official reason: "The Department of Homeland Security did not explain the reason for this question, and it is not clear why any terrorist, spy, saboteur or mass murderer would answer “yes.” Doing so, whether or not by mistake, does not mean that the person will be banned from the United States, but it doesn’t help." (https://www.nytimes.com/2018/11/30/world/europe/terrorist-qu...)

For the same reason that it is easier to arrest drug dealers, pimps, mafia dons, etc… on tax evasion charges than the more immediate crimes they committed.