1. The Irish spoke English.
2. The Irish were both Western and white.
3. Even so, I think that they were still good arguments back then. What was the effect of the large numbers of Irish people coming into the US on work conditions and wages?
1. Yes, Gaelige (gwale-guh), or Irish Gaelic, saw a steep decline, as a result of both the Anglicization of the Protestant community (including Irish, Ulster-Scots, and Anglo-Irish), as well Gaelige being quasi-illegal (lots of back-and-forth with the language going back to the Statutes of Kilkenny, and seeing direct assault during The Protestant Ascendancy). The average Irish Catholic arriving in the US prior to the Gaelic Revival around 1877 spoke precious little Gaelige, if any.
2. I would advise you to the read the book "How the Irish became White" by Noel Ignatiev. The Protestants which arrived were treated with either indifference or certain distrust, and are typically referred to as "Lace Curtain Irish". Many of these "Prods" were Ulster-Scots (known in North America as Scot-Irish), and there were quite a number of US Presidents descended from them (Andrew Jackson, James Buchanan, Ulysses Grant just to name a few). Roman Catholic Irish, on the other hand, were treated with severe disdain, and were often referred to as "Shanty Irish", especially when large amounts of them came over in the Coffin Ships during The Blight (Irish potato famines). More than one US newspaper decried that American cities were being overtaken by "waves of the 'n-word' Irish". These Catholics were seen as violent drunks, and police carriages in cities with large Irish populations became known as "Paddy Wagons", a term still in use.
3. The biggest concern Americans had was the fact that the majority of Irish immigrants were Roman Catholic and uneducated (not their fault. Read about Irish Catholics in Ireland immediately following the Williamite Wars and the Protestant Ascendancy). The "No Pope Of Rome" mentality was alive and well in the US at the time (German immigrants were often hated for the same reason). Irish Catholics became desperate for work, as more than one place of business had a sign outside saying "No Irish Need Apply", leading to one of the earliest Irish folk songs written in the US. The Irish often forund work in the police departments, as police work was not the glorified, good career it is today. Police work was incredibly dangerous and pitifully low-paying. However, most metropolitan police forces accepted the Irish, and there are now "dynasties" in the East Coast departments (law enforcement families).
While my father's family has been in this country since the 1880's (of County Wicklow, Ireland, as well as the Scottish Highlands), my mother's parents immigrated here from County Fermanagh, Northern Ireland, in 1949, and did not face the prejudices that the Irish immigrants before them did (while my mother was born here, here two oldest siblings were born in Enniskillen Town, County Fermanagh).