Although Thailand may have more freedom of speech than any of the countries it shares a border with, it nevertheless lacks freedom of speech. Some aspects of the political history of the country are very, very difficult to talk about, within the bounds of what's permissible (I've just seen a few statements on Wikipedia that would be punishable in Thailand).
The feelings of the Thais toward Laos are too intense to be changed by facts. Is there anything I can compare this to in contemporary Europe? The English don't care nearly so much about the Scottish, nor do the Spanish have any such feeling toward the Portuguese, despite the long histories of war and rivalry in both cases. Perhaps the only comparison would be the feelings that Russians have toward Crimea, in now claiming the latter as a province: more than just a claim that in the future they should form one-and-the-same country, the attitude is based on a presumption that the smaller country never had a right to exist, and that the border separating them only came about by trickery. The sense that --somehow-- both sides were cheated out of their national destiny is strong in Thailand; it would make more sense if this sentiment were paired with the notion that the Thai and Lao are "one race" (as the Russians consider themselves the same race as Crimean Russians --although not the same as the Crimean Tatars) but, instead, it is juxtaposed to the very fundamental belief that the Thai and Lao are two separate races, and, unsurprisingly, the Thais consider themselves racially superior to the Lao.
An old book that I recently rediscovered on Archive.org (link below) provides a reminder of a terrible truth that is inconvenient to both sides, as they now write the 19th century's history.
