Galactus tends to be one of the most contriversial characters in the MU. One story can have him be the antagonist with the next him being an ally. Most people just know him as a cosmic power house that feeds on planets regardless of the planet's status and whether it is inhabited or not.
Facts/Questions to consider:
1. Galactus has been stated to serve as the balance between life and death. It has been several times implied that it would be a very bad thing for the universe in the long-term if he were to die. This has been confirmed by Eternity itself.
2. It has been stated numerous times that Galactus is beyond human concepts of morality due to being a natural force.
3. What Galactus can feed upon varies from story to story, but generally he can only feed on planets that meet certain unspecified conditions.
4. Galactus only feeds or does what is needed for him to survive. He has no interest in ruling the universe or laying waste to galaxies for fun like Tyrant, Thanos, Annihlus, or other villains.
5. Galactus once upon a time tried to avoid feeding on inhabited planets, but two things changed. Galactus had to start feeding more often and as sentient life spread across the universe it often colonized every thing it came across including all the planets he can feed upon.
6. Galactus's hunger has been stated to cause him great pain and drive him in a near-frenzy at times.
7. In the past, several heralds have tried to steer him away from inhabited worlds, but eventually develop a crisis of conscience. The meaner ones have less scruples, but are insane or like killing. So having the right herald is difficult if not impossible.
8. If Galactus did try to give planets time to evacuate, would they just try to kill him instead?
9. If Galactus was more specific on what planets he fed upon, such as limiting himself just to hostile races, would this not betray his original neutral purpose?
10. Don't most interstellar wars cause more destruction (War of Kings with Vulcan blowing up planets, Annhilation Wave, Operaton: Galactic storm and the destruction of the Kree Galaxy) in a year than Galactus does in a hundreds?
11. Looking at it from Galactus's point of view, with having lived for billions of years and power, knowlege and technology far beyond what most being can conceive doesn't that in a way make him superior to beings that only live for a hundred years or so?
12. Last fact, it has been stated he is destined to one day give back far more than he has taken.
So, in your opinion if Galactus evil, beyond such labels, or just a victim of circumstance despite all of his power?