Wyll made a pact with a cambion for his powers. Thats the entire list of things that I can add to the 'bad things Wyll did' list so far. If that makes him evil every warlock is evil 😂
Well, every fiendish warlock anyway. You can't be a fiend without being EVIL. Though the Fiend pact warlocks can be good (Warlock and Patron trying to kill each other is semi-frequent story arc.
The other pacts aren't necessarily evil patrons (though Undying and Great Old One patrons are dominated by evil types with a fair speckling of Neutrals and almost no goods outside certain campaign settings such as the Undying Court in Eberron.)