[ghaff]

Assuming the country in question requires an explicit business visa for you as an $X citizen to attend a conference, it's probably not a good idea to lie--even though you also probably won't get caught. (Many countries don't draw a distinction between tourism and a routine business trip or some combination thereof for at least some passports however.)

(And as the sibling comment notes, if you're just dropping in for a quick conference and heading home again, that probably is suspicious as a tourist.)