Regarding mass starvation - no I don't believe Alexander's army made a habit of this. The march back from India is very likely to have left some populations in that state though. My reading of Nearchus' account leaves little room for other conclusions. Story after story of small villages with few resources, which Alexander's men strip bare of dates, grain, fish or meat. Whether the natives tried to placate them with gifts or not, it did not matter. We are talking about the Gedrosian desert here, so food was not easy to come by for Alexander's men and it would not have been so for the locals after they left. Barring miracles, mass starvation seems overwhelmingly likely at least for some of these populations. I believe that the Gedrosian march did not go according to plan. But the benevolent conqueror thesis it does not support. I'll quote just one of the many stories.
As for Alexander's motivations to conquer India, it's important to remember that India had much wealth to offer. The Persians had conquered parts of India before Alexander, presumably with a lustful eye towards its jewels, elephants, wood, precious metal etc. Most of the territory Alexander had conquered in India had at some point been under Persian rule, though temporarily. Why are Alexander's motives more likely to be romantic than any of the Achaemenids who had invaded, conquered or ruled India?Arrian wrote:Thence about midnight they sailed and came to a harbour Cophas, after a voyage of about four hundred stades; here dwelt fishermen, with small and feeble boats; and they did not row with their oars on a rowlock, as the Greeks do, but as you do in a river, propelling the water on this side or that like labourers digging I the soil. At the harbour was abundant pure water. About the first watch they weighed anchor and arrived at Cyiza, after a passage of eight hundred stades, where there was a desert beach and a heavy surf. Here, therefore, they anchored, and each ship took its own meal. Thence they voyaged five hundred stades and arrived at a small town built near the shore on a hill. Nearchus, who imagined that the district must be tilled, told Archias of Pella, son of Anaxidotus, who was sailing with Nearchus, and was a notable Macedonian, that they must surprise the town, since he had no hope that the natives would give the army provisions of their good-will; while he could not capture the town by force, but this would require a siege and much delay; while they in the meanwhile were short of provisions. But that the land did produce corn he could gather from the straw which they saw lying deep near the beach. When they had come to this resolve, Nearchus bade the fleet in general to get ready as if to go to sea; and Archias, in his place, made all ready for the voyage; but Nearchus himself was left behind with a single ship and went off as if to have a look at the town.
As Nearchus approached the walls, the natives brought him, in a friendly way, gifts from the city; tunny-fish baked in earthen pans; for there dwell the westernmost of the Fish-eating tribes, and were the first whom the Greeks had seen cooking their food; and they brought also a few cakes and dates from the palms. Nearchus said that he accepted these gratefully; and desired to visit the town, and they permitted him to enter. But as soon as he passed inside the gates, he bade two of the archers to occupy the postern, while he and two others, and the interpreter, mounted the wall on this side and signalled to Archias and his men as had been arranged: that Nearchus should signal, and Archias understand and do what had been ordered. On seeing the signal the Macedonians beached their ships with all speed; they leapt in haste into the sea, while the natives, astounded at this manoeuvre, ran to their arms. The interpreter with Nearchus cried out that they should give corn to the army, if they wanted to save their city; and the natives replied that they had none, and at the same time attacked the wall. But the archers with Nearchus shooting from above easily held them up. When, however, the natives saw that their town was already occupied and almost on the way to be enslaved, they begged Nearchus to take what corn they had and retire, but not to destroy the town. Nearchus, however, bade Archias to seize the gates and the neighbouring wall; but he sent with the natives some soldiers to see whether they would without any trick reveal their corn. They showed freely their flour, ground down from the dried fish; but only a small quantity of corn and barley. In fact they used as flour what they got from the fish; and loaves of corn flour they used as a delicacy. When, however, they had shown all they had, the Greeks provisioned themselves from what was there, and put to sea, anchoring by a headland which the inhabitants regarded as sacred to the Sun: the headland was called Bageia.