Ireland’s love affair with pub and pint is sparking national soul-searching as never before because of an unofficial holiday dreamed up by Guinness. Thursday’s celebrations of Arthur’s Day, honoring the 18th-century founder of Ireland’s quintessential drink, feature surprise musical performances in 815 pubs and clubs across Ireland as well as concerts worldwide from Malaysia to Jamaica. … Many pubs are offering free pints of the dark brown stout at 5:59 p.m.—a reference to the founding of Guinness in 1759 … But this year, Guinness has been put on the defensive amid surging protests that Arthur’s Day is compounding an alcoholic...