You seem to be conflating the concepts of "dictator" and "genocidal maniac".
Those are not the same things.
As for his actions against white Zimbabweans; well, you must understand that
pre-1980 Zimbabwe (called Rhodesia, or Southern Rhodesia before 1965) was not
just a racist nation with racial segregation laws, but that about half of the
country was allocated to white minority by law. Even in 1997 much (about 70%) of the country's fertile agricultural land was still owned by whites (by then just 0.6% of the population).
This isn't to say that the land reform programs were a good idea by any
standard, but they're not borne out of blind hatred against whites like your
question suggests. After 1980 Mugabe's government took pains to ensure fair
treatment for whites. The original plan to re-distribute land was by legal and fair purchase, not by forced seizure. This didn't really take off due to lack of funds, but if Mugabe was truly as anti-white as you suggest he would have acted much sooner against the whites.
It wasn't until the mid-90s that things really went down the crapper. Mugabe had traveled the familiar route that Mao, Qaddafi, Castro, and many others had walked: from fighting an oppressive regime, to becoming the slightly crazed head of an oppressive regime themselves obsessed with staying in power.
The economy was struggling and opposition against Mugabe was growing, and he
increasingly started to use the white population and Western countries as
scapegoats for Zimbabwe's problems, eventually resulting in the famous – and
disastrous – programs where land from white farmers was confiscated and given to (usually inexperienced) black farmers.
Much of this seems to be distraction and 'scapegoat-ism' to keep in power just as much as anything else; just as Mugabe's increasingly anti-Gay rhetoric is.
He has even characterized himself as Hitler.
No, he hasn't. The full quote:
I am still the Hitler of the time. This Hitler has only one objective, justice for his own people, sovereignty for his people, recognition of the independence of his people, and their right to their resources. If that is Hitler, then let me be a Hitler tenfold. Ten times, that is what we stand for.
This was in response to some British newspapers comparing him to Hitler. He just told them to stuff it. It's not exactly subtle, but he certainly didn't
"characterize himself as Hitler".