I don’t know much about H.L. Mencken. I have heard him referred to on Frasier and I have some vague idea that he was a ‘word maven’, an expert on the American English language. The fact is that Mencken isn’t really a big name over here. In Ireland, he is not much quoted and is certainly far less famous than Dorothy Parker or Mark Twain. Cassidy and people like him are fond of quoting H.L. Mencken as an example of discrimination against the Irish, because he denied the extent of Irish influence on English and said that ‘perhaps speakeasy, shillelagh and smithereens exhaust the list.’ From what I have read online, he does seem to have been a racist and a rather unpleasant man and the quote above about the Irish is obviously not genuinely about linguistics. As an expert on English, I think he would have known that speakeasy isn’t an Irish word (it comes from the English words speak and easy!), though its synonym shebeen is. The fact is that Mencken’s glib comment has a narrative in it. The Irish drink, fight and wreck things. They go to the speakeasy, hit one another with shillelaghs and smash things to smithereens.
However, to take the fact of Mencken’s snobbish, racist attitude to the Irish and other minorities and use it to suggest that Webster’s and the Oxford English Dictionary have conspired against words from the Irish language only makes sense if you buy Cassidy’s idiotic claims wholesale. It is quite plain that there is no evidence of a large number of words derived from Irish in the English language and those that do exist, like banshee, usker, whiskey, poteen, esker, drumlin, shebeen, galore, ogham and tanist are already in the dictionaries. If you gathered a large number of linguists together and asked them to look at the Irish contribution to English again, it is unlikely that they would turn up more than a couple of extra words. The reason why the lexicographers are reluctant to take Cassidy’s claims seriously is that they are rubbish and Cassidy was a fraud. There is no conspiracy against words of Irish language origin. It is just a smokescreen, a ruse invented by Cassidy himself so that gullible people would regard academic criticism as proof of Cassidy’s rightness rather than proof of his stupidity and dishonesty.