Why the Romans came to dominate the Mediterranean has been a problem since Virgil. There have been a bunch of theories (Virgil attributed Rome's military success to divine will) and exceptional aggression is only one possible theory.

Harris might be the modern scholar most committed to that position. He published War and Imperialism in Republican Rome 327-70 B.C. in 1979. He is reacting against the prevalent position of "defensive imperialism" - that is the idea that Rome got its empire through defense of itself and its allies, which is another ancient theory. In fact, the last section of his book is an examination of the wars conducted in the period of study, in which he attempts to debunk the ancient justifications given for them to show "defensive" actions were really aggressive.

His thesis is that Roman culture at all levels had military violence built into it. Here is Sherwin-White's summary from his 1980 review:

The thesis of this book is that Roman aristocrats found their greatest satisfaction in waging war as a means of enrichment and personal advancement - a view that few will dispute - and that the Senate as their institutional instrument deliberately organized an unceasing series of aggressive wars for the perpetual expansion of Roman power and wealth throughout the two hundred and fifty years down to 70 B.C.

But Harris goes further and argues that the structure of everyday Roman life also provided motivation for the rank-and-file to engage in continual warfare in a way that no other Mediterranean state engaged in. War is built into political life, but also religious life and economic life. The most important political matters were the election of military commanders - consuls and praetors. War provided plunder, land, and slaves to work the land for farmers. Religious ceremonies gave legitimacy to war.

Harris' view isn't universally accepted. Sherwin-White's review (already mentioned) is pretty scathing and openly accuses Harris of being reductive. My own observation is that, writing in 1979, Harris has some experience with apparently unjustifiable imperial wars. In his introduction he disavows political motivation for presenting his view, and in fact justifies his book by accusing others of defending their own politics through the lens of Roman history, but I have to wonder what around 1979 might make someone start thinking about brutally imperialistic states fighting unjustified wars.

The most direct reaction to Harris I know is Eckstein, 2006, Mediterranean Anarchy, Interstate War, and the Rise of Rome. Here is a free review. For the record, I love this book. I have a background in IR and I love seeing system-level analysis put to work to understand Roman history.

Eckstein argued that Rome wasn't any more warlike that anyone else around - Harris didn't actually look at the other cultures in the Mediterranean when he did his analysis of Rome. Instead, the international system of the post-Alexander Mediterranean positioned a small power like Rome to exploit a multi-polar world in which the great Hellenistic states were too busy fighting each other to respond to a rising peripheral power until it was too late. Quillin, who wrote the review I linked (and whom I don't know from anything else) thinks Eckstein is just as reductive as Harris, and Eckstein's use of a political theory meant to understand the Cold War has raised concerns elsewhere, but as I said I'm quite a fan of this book.

Rosenstein also has a bunch of articles and a book about aristocratic competition and war. All together he takes an approach that sees Rome's aristocratic life as a driver of warfare without the need for it to pervade the culture as Harris argues. A crass way of putting it is winning wars is good for winning elections. The competition system also managed to find ways not to punish failure, so war came at no cost to the aristocrat.

Bottom line, the assumption that Rome was especially aggressive is not well accepted and there are lots of competing theories that have various levels of traction.