This question is hotly disputed, almost as much as 'Why did the Roman Empire fall?'

Lemme preface this by saying that the life and death of Julius Caesar have been heavily polemicized by people of all kinds of different ideologies and world views. The Senatorial elites of Rome wrote about him one way because of their perspective, and the supporters of the Imperial regime tended to write about him another way. The founders of American democracy put checks on the office of the presidency to try and prevent presidents from becoming dictators, like Caesar did, (such as impeachment, which they explicitly included so that there would be a legal alternative to tyrannicide) and yet some of the founding fathers revered Caesar. Alexander Hamilton believed Caesar was the greatest man who ever lived.

So why is it that in today's classrooms we wholesale endorse the idea that Caesar was an unjust tyrant who overthrew a great Republic, solely for his own benefit, and that this was an unarguably 'bad' thing?

Because it fits the narrative that the rich political elites of our day and age want to tell about how democracies should function: ie, that rich elites with all the money should run everything however they want (including suppressing reforms and bleeding the general public dry as long as they do it on the sly) and that challenging or overthrowing that system in favor of reforming it to better meet the needs of the people is absolutely the worse and more morally heinous of the two alternatives.

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Rome was Republic, but it was also an exclusive oligarchy; a plutocracy. Only the super rich super elites held any real power, and in fact by Caesar's day the system had become so corrupt and full of graft, bribery, and cheating that it was essentially a kleptocracy, like Putin's Russia.

It had a very rigid, top-down social and political hierarchy. ALL political power was held and exercised by members of the top two political classes, the Senatorial and Equite orders. In today's parlance they're roughly comparable to the top 1% and the top 10% of the richest people. All magistrates were chosen from these elites. To be in either order, you had to have a very insanely ludicrous amount of money. To be in the top bracket, you also needed to have served or had a relative who had served in the Senate. New men were extremely rare, and looked down upon.

In addition to holding and wielding all political power, these top two classes also controlled all religious power and most of the voting power as well: although there were public assemblies, the vote of the top two classes could usually carry a vote as long as they all voted in unison, which meant that in matters that negatively affected them, the elite classes only had to make sure all their voting members voted according to the party line to win.

This collection of powers meant that the elites could basically push the general public around at will. In practical effect, this meant that by Caesar's time, the elite had come to own the overwhelming majority of farming land (leading to the mass displacement of hundreds of thousands of Romano Italians), the basis of all wealth in the ancient world, and were running corrupt lending schemes that forced more and more into debt, and then into either selling their land or, even worse, being forced to essentially sell themselves or their family members into slavery to cover the costs of their debts.

Now, there was one political office that in theory existed to protect the people. The people's tribunes had the power to propose legislation or veto any legislation or governmental action that they thought was unjust or injurious to the people. However, since the Tribunes could, like all the other magistrates, only come from one of the two top socio-political classes, it meant that in practice, MOST of the time the tribunes didn't rock the boat for their own social classes much.

But there were exceptions. Every once in a while, a reforming tribune would come along with an agenda aimed at making life better for the people. This normally took one of four forms: forcing land redistribution on the elites (taking lands from them - usually lands they had no legal rights to in the first place, but sometimes going further and taking back lands they had used the legal system to financially coerce individual farmers off of - and giving them to people who needed them), attacking debt slavery, forcing the state to pay for free food for the very poorest, and attacking corruption and graft on the part of the elites.

Why did they do this? Why attack the corruption and greed of their own social classes, why help the poor everyday citizens?

Well, in the view of the elite upper classes, the accusation was usually that the tribunes doing so were power-hungry demagogues who (rightly) believed that they could get the support of the people and catapult themselves into positions of great power and influence by giving the people things they wanted, for no other reason than that they were power-hungry. By dividing the elite vote and winning the support of the people, these reformer tribunes could advance their agenda over the objections of the rest of the elite.

On the other hand, for their part, the reforming tribunes generally maintained that they were for good government, the idea that government had a responsibility to serve ALL citizens, not just the super elite, and that the elite had been using their chokehold on power to unjustly oppress the common people and that they were just righting the scales.

Who was telling the truth? It's hard to say for sure. Most of the surviving historical and epistolary accounts we have come from members of the elite who were very much for corruption, graft, and greed - in moderation, and it's hard to deny the fact that buying up or seizing ALL the land (even land you have no legal right to) and forcing people into ruinous debt so that you can extort their property from them or even sell them into slavery are pretty incredible acts of greed and corruption, so it can't really be said that any of our surviving sources from that camp have unbiased views, and it seems highly unlikely to the point of impossibility that EVERY single person who ran for people's tribune on a platform of reform was motivated solely by personal gain, because that implies that ALL Romans were completely without empathy or sympathy for their fellow citizens, and that not only seems ridiculously improbable but flies in the face of later examples from the Roman Imperial period, when Emperors like Trajan, Hadrian, and Marcus Aurelius, who were fully secure in their power and had no need to buy public support but still believed in good governance for its own sake. But, it's equally unlikely that all the Reformers put the people completely ahead of their own interests. Most likely there was a balance between the interest in good governance and the needs of the people on the one hand and personal advancement and ambition on the other on the part of most of the reformers.

In the end, though, things usually did not go well for the reformers (yet another reason, in my opinion, to suspect that the reformers were likely motivated-at least in part-by the desire to do good for the people and the state, and not solely personal glory). Many of them ended up dead. When a reformer achieved a certain level of success in pushing their reforms through over elite opposition, the elites would routinely resort to back alley violence, character assassination, drummed up criminal charges, or state-sanctioned murder to take the reformer down. The result was that the elites managed to keep the reformers from gaining too much ground and intimidated other potential reformers into keeping their heads down. After a little time had passed, most reforms were reversed or legislated into ineffectualness, and the elites went right back to their corruption, graft, and greed.

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