Gods of disease are also often gods of healing, or vice versa, because you pray to them to
not get you sick, or to appease them so they lift the sickness. Take Apollo, for example.
This applies to other gods of things people fear. Yes, they are responsible for the bad, scary thing, but they are also responsible for keeping the bad, scary thing
away from you. So, it depends on the circumstances. Gods are representations, personifications of forces of nature, but at the end of the day, aren't the same as actual people. You don't call a force of nature evil, it simply is. And sometimes nature brings good things, boons, and sometimes it's violent and dangerous. So a god is defined by the temperament of the thing they represent, and that often changes depending on geographical location. For example, a god of the sea in a place where the seas are are dangerous and stormy, will be characterized as more wrathful and fickle, whereas elsewhere, where the seas are gentle and offer lots of fish, the god of the sea will be portrayed as generous.
Usually people say the sun god, the river god and harvest god are always good. And usually the death god or darkness god are evil, despite them just doing their jobs. But what would you consider an evil god? What is your justification for this god being evil?
A sun god may be feared in the desert for the heat, blinding light, and danger, a river god may be feared if the river is rapid and dangerous, and prone to flooding, without offering the fertilization that occurs from other flooding rivers. A harvest god might be seen as more antagonistic in a place where the soil is unfertile and hard to grow crops in.
And a death god might be quite respected and loved, depending on the culture's view of death. If they think the afterlife is a big party, then the god who rules over that isn't bad. And a god of darkness may also be a god of sleep, of rest. Of relief from the heat of the day.
