I will concede that there are many mainstream Catholics who are less than kind when discussing those Catholics who give their allegiance to the Society of St. Pius X (SSPX). I hope that you will also concede that SSPX Catholics are also guilty of the very thing they complain of when they use pejoratives such as “neo-conservative,” “neo-Catholic,” and “Novus Ordo Catholic” to refer to Catholics who do not have a particular devotion to Traditionalist Roman Catholicism but are otherwise orthodox.
As to your question, it may be that discussions between mainstream and SSPX Catholics are acrimonious and strained because the excommunication of the SSPX bishops was so recent (1988) and only lifted even more recently (just this year). There has been 500 years of callusing on the wounds between Catholics and Protestants that has not had a chance to occur between orthodox Catholics and the SSPX. Certainly we may hope that the healing of the rift between the Church and the SSPX will not take 500 years to accomplish, but in the meantime tensions are likely to remain high.