Honestly, Alexander and Phillip II killed more Argeads than all the Diadochoi put together. Philip II executed at least one half-brother during his early years, possibly two more in the Chalkidike (I don't have my Diodorus with me at the moment, so I can't say if he explicitly killed them or if they "mysteriously" disappeared from the record). Alexander likewise did away with Amyntas IV and his own half-brother and sister, the children of Eurydike and Philip. That's at least four, possibly six, shared between two individuals, not counting any I've forgotten (obviously). Alexander and Philip aren't exactly blameless when it comes to the lack of potential Argead heirs after Alexander's death...
Throw in the fact that Alexander's Casus Belli on the Persian Empire was "Lol, they burned a temple once," and "I can, so why not?" I have literally no sympathy for the Argead family as a whole. I feel bad for the various royal women executed in the course of the Wars of the Diadochoi (seriously, Cleopatra and Cyane did nothing wrong, they were just born with the wrong bloodline), but that's on a case-by-case basis.
It was just the way of Macedonian politics back then anyway. Although Alexander's "cb" on the Persians was probably based in a lot more than "they burned a temple once". The Persians had tried to invade Greece of multiple occasions previously, with Macedonia being a victim of that.
It is not like one needed a valid excuse to go to war when the entire aristocracy and nation at large supports it. Alexander and his father amassed truly gigantic armies, and contended with the might of Persia, proving victorious in the end.
The moral of the story is not to feel necessarily bad for the Argeads, but you can feel sympathy, certainly. They are the epitome of a cautionary tale, and Alexander proved to be mightier then the classical greats that came before him. Heracles may have killed a Hydra, but who else but Alexander destroyed the Kingdom of Kingdoms? It is tragic what happened to him, and so young. The line of his bloodline is especially telling. Imagine, if say Alexander had lived to a healthy life, if not an overly generous one, of another thirty years? These were the greatest plans for his reign, as dictated by Diodorus of Sicily.
-It was intended to build 1,000 warships larger than triremes in Phoenicia, Syria, Cilicia and Cyprus for the expedition against the Carthaginians and the other inhabitants of the coastal area of Africa, Iberia and the neighboring coasts as far as Sicily; to build a coastal road in Africa as far as the Pillars of Heracles, and, as required by such a large expedition, to build harbors and shipyards at suitable places.
- to build six expensive temples at a cost of 315 ton silver each (the temples just mentioned were to be built at Delos, Delphi and Dodona, and in Macedonia there was to be a temple of Zeus at Dion, one of Artemis Tauropolos at Amphipolis, and at Cyrnus one of Athena);
-in addition, to settle cities and transplant populations from Asia to Europe and vice versa from Europe to Asia, to bring the largest continents through intermarriage and ties of kinship to a common harmony and feeling of friendship.
-Likewise there was to be built at Troy a temple of Athena which could never be excelled in size by any other.
-A tomb for his father Philip was to be constructed which would be as large as the greatest pyramids in Egypt.
It's clear that Alexander intended to conquer the known world. With no infighting, not even the Mauryan Empire could disturb him, and even if the soldiers that were stationed along the Indus were thrown from rebellion, an united Empire under Alexander would no doubt have exponential impact and status on our world the further he had lived. Just think of what the cultural heritage that the Hellenes provided, lasting more then two thousand years as a major political power until the fall of Constaninople. Even then, the vitality of the Catholic Church, which had necessary traditions and foundation within Rome, itself taking large part from the Greeks. Can anyone deny that Alexander is not a sympathetic character? He is last greek hero of antiquity, a beacon of civilization and western thought. He was mentored by Aristotle himself! Anyone who doubts his legacy for some perfumed persians.. Blasphemy.