There is a bit of a mix up here. The "barbarians" thing is likely a reference to one Mussolini's speech in Bari on September 6^th 1934 when he proclaimed how the Italians (the fascists, that is) "could look with supreme disdain at certain transalpine doctrines [...] of people who were ignorant of written language, back when Rome, etc. etc.".

Engelbert Dollfuss - the Austrian chancellor and personal friend of Mussolini - had been murdered on July 25^th 1934. Mussolini had reacted (postured) strongly: threatening a military intervention in case the Nazis had attempted to seize power in Austria and actually instructing two divisions on the border to pre-mobilize.

But that was not the Anschluss, which only took place four years later in March 1938; after the Germans had gained the Italian approval for it. As of 1934, the initiative against Dollfuss had been a spontaneous coup attempt by the Austrian Nazis and - while I can't say that no one in Germany was aware of it - it appears that Hitler was quite incensed with the rash decision.

For a few days the Italian themselves weren't really sure what to make of it and even if Mussolini was ready to blame Hitler, the Italian diplomats were of the opinion that it had been a last attempt of Röhm's faction to destabilize Hitler's government [they had this idea that Röhm represented the extreme Nazi wing and Hitler the moderate one]. Anyways the Italians were much relieved to see the appointment of Franz von Papen to Austrian ambassador - being in their eyes the former chancellor an influential and moderate figure - while in reality he was no longer really that influential and quite adamantly favorable to the "anschluss".

Which was still a big no-no for Mussolini; Austria was the door to the Balkans, an area where Italy had traditionally contrasting interests with the German powers. With this in mind, Mussolini went to the nice town of Stresa, on the banks of the Lake Maggiore, in order to discuss the issue with the French and British Prime Ministers Pierre Laval and Ramsay McDonald. And in April 1935 they again proclaimed their intention of preserving the Austrian independence.

Except you are wrong about Mussolini - and he was totally the kind of guy who let's go of a grudge if he thinks it's convenient, or necessary. While Mussolini did hold a general view of history as a process of development driven by conflict among cultures-peoples-nations, there was no "absolute conflict" like those occupying Hitler's mind. Opposition was driven by circumstances and even ideological opposition was a matter of convenience; in this regard Mussolini always saw himself as a master of ideologies, not a slave to one. And his criticism of National Socialism came from the necessity to show both the prominence and primogeniture of Italian fascism and to prove the resolve of the Fascist Regime.

There was another theater where Mussolini was anxious to prove its mettle - around the time of the Stresa agreements, Italy had already resumed preparations for a military occupation of Ethiopia (Mussolini's instruction is from December 1934). At the same time, there were talks of an extended protectorate with direct occupation of a few zones under Italian, French and British supervision (the so called Laval-Hoare plan) to prevent a full scale conflict. Except a full scale conflict would have worked better as a proof of strenght - and Mussolini seemed to become convinced that a decisive action (one thing he really liked) would have met with little resistance from the British and French. Which is what eventually happened since, even with the economical sanctions passed in consequence of the Italian aggression, the effects on the Italian economy were modest and completely ineffective before 1937-38, when Italy begun to suffer the depletion of some important resources during the Spanish Intervention.

At this point Italy and Germany had already become closer; more so Mussolini had already given up on his Stresa agreement when he had made the choice to attack Ethiopia - in all likelyhood he didn't believe the French and British were truly committed to prevent the "anschluss", nor that Italy could do so alone. It was more convenient to seek an agreement with the Germans for the fact to happen on good terms; which is what he obtained, even if it was a very little price for what the Italian diplomacy would have considered a fatal threat just a few years before, with the German reassurances over the matter of the German residented of Italian Trentine.

There were of course many more aspects to the whole process - but, in short, that seems to have been Mussolini's reasoning behind the choice to approve the "anschluss".