It seems to me there is more to being good than having good customer service, which is the only evidence you mention here.
Even if I had no evidence, my default assumption would be that they were good until confronted with significant evidence that they were evil. And between good and evil there's a nice-sized neutral middle area which it appears you have transited in one fell swoop based on your sole piece of evidence.
I'm not sure what other evidence of goodness you seek than customers' experiences with them. I have found their prices competitive - as another poster said - lower on some items and higher on others. They have treated me fairly. I don't believe that they are engaged in any immoral enterprises. I agree it would be nice if they cooperated with Octopart but to say that makes them evil is absurdly hyperbolic.
I can immediately think of some (non-evil) reasons for Digi-Key to prefer not to have Octopart include its pricing. It has invested in a web site which provides an excellent user experience and they would prefer not to make it easier for customers to use Digi-Key's web site as a reference manual for lower cost competitors (whether or not you believe this is inevitable). They would like to avoid doing business with customers who are concerned solely about price. They would like customers to purchase their higher-margin items based on past experience purchasing lower-margin items even though the higher-margin items might be cheaper elsewhere.
Your theories about why Digi-Key wouldn't want their prices to be publicly known are very inventive, but Occam's razor suggests the explanation is what is usually is in such situations: They are trying to suppress competition.
First, bodega and convenience store owners don't order smokes from Philip Morris, they get all their stuff from various distributors. The stores themselves are usually locked into one distributor for junk food/smokes and another for liquor. Depending on how low you go on the convenience store food chain, often times the "distributor" is just a guy with a truck. Thus I'm not sure a good online business could be made aggregating the various prices of cigarette distributors. A useful startup idea would be a location-based mobile app that would tell you which bodega nearest you carries the cheapest cigarettes. You could make it non-evil by selling ads for nicotine replacement therapy that you would have to click through before getting the price for a hardpack.
As far as Digi-Key goes, they aren't the biggest distributor of electronic components... maybe in the top 20, or maybe top 10. However,they probably ARE the biggest distributor that will sell small lots to hobbyists. They are also one of the major employers in a small town in a rural area that has had a flat economy for decades. The only other employer of note is the snowmobile factory. Most of the money in the area is made by landowners who are paid your tax dollars to not farm their land, or else grow sugarbeets, one of the least efficient ways of obtaining sugar. Since they would have had to pay the most, those same farmers voted against school improvement bonds every year I lived there...so I'm going to have to go with "evil" on stupid farm subsidies but now I'm really digressing...
I'm going to have to vote "not evil" for Digi-Key. They know they are competing on price and are doing what they can to avoid losing business. If sales go south, they have to lay people off. Most of the employees don't have anywhere else to go find work. From my limited personal experience, there isn't a CEO caste at Digi-Key with golden parachutes who all stay rich whether or not the company does well. If they lose business, everyone gets fucked. I'm guessing they are cockblocking Octopart out of fear. This sucks for Octopart and is inconvenient for people prototyping electronics, but is it evil?
EDIT: what's really evil is that unknown or expired link error!
When Microsoft accused Linux of violating 50 software patents, most people thought they were pretty evil. The claims were frivolous and their aim was to preserve their market share at the expense of consumers. Likewise, Digi-Key makes the frivolous claim that by displaying their public information and linking to their webpage, Octopart is acting illegally.
This is not a debate about whether Digi-Key is good for the town of Thief River Falls or if Digi-Key should be making money. They have as much right to make money and keep their employees happy as Microsoft does, but when they use their muscle to wrongfully stifle innovation at the expense of consumers, it shouldn't be surprising that some people would call them 'evil'.
What is public about it?
It looks like there is a larger back story to this than was originally obvious to me from your essay and that has loomed very large in your estimation of Digikey's character. Framing it as a David and Goliath morality play is good marketing but I think a more nuanced view is reasonable - they're somewhat less good than I originally believed.
The parts supply industry is not an industry of monopolies. There are a few large names--Grainger, McMaster-Carr, MSC, Digi-Key--that probably account for 25% of the market, and then a very, very, very long list of names most people have never heard of.
Ironically, Ma & Pa Electronics are frequently the ones with the highest prices. Large distributors like Digi-Key are often less expensive than small local shops.
Yes, some companies are running about doing things that are obviously good (feeding the hungry, clothing the poor), but for everyone else, I think 'good customer service' is the rarest and best compliment, because it implies a positive relationship.
You make a good point; I don't think I can argue against what Octopart is trying to do from any kind of good vs. evil ethical standpoint. However, I can understand a business such as Digi-Key wanting to maintain control, and they could easily argue it is for the benefit of the customer. For example, when a customer searches Octopart, are they going to also get a list of complementary parts from each supplier? I doubt it. What about helpful charts, material safety data sheets, and CAD schematics? If someone was just scraping my site and hijacking the search functionality but failing to deliver the rest, I'm not sure I'd want my name attached either.
Of course this is really coming at it from the wrong level. The truth is that Digi-Key can simply ignore you, and it doesn't hurt them in the slightest. And while doing so, they can be sure they aren't reaping any of the negative consequences of being associated with you either.