There's the legal aspect, the ethical aspect, and the practical aspect.

When I launched acrewardsearcher.cowtool.com, you didn't even need to log in to use it. Then I noticed... issues. But without people logging in, I couldn't even track the issues very easily. So I required you to make a free account and log in. Then it became pretty clear who was a bot and who was real, so I banned the bots. But they just made new accounts. So I restricted access to new accounts (but then that was hurting the ability of people to use other cowtools, so I changed it so you could make an account, just without access to the reward search). And then if I blocked you, you were basically done (though there was a black market for cowtool accounts).

In my case, there was a tangible cost to increased load on cowtool. But it was very aligned with AC's "costs", in that as my traffic went up, my costs (and presumably AC's) went up. But my revenue stayed at 0. So everything I did on that front benefited both entities.

But if I had charged for it... well now I'm incurring costs, but making a profit. But I'd be causing AC to incur costs as well. And now the incentives are misaligned. I'd want more traffic, because it would mean more revenue. But AC would want less traffic, because it means increased costs.

But a lot of people seem to be missing the bigger picture that they've clearly stated numerous times. Let me throw some speculation into it (i.e. I don't know this for sure, but it's plausible based on what they said).

The typical Aeroplan customer is a FOTSG who lives in Canada. Presumably most of their family are in Canada. Their searches are YYJ-YHZ or similar. Those searches can be done within AC's system. There are costs for those searches, but they're probably very low.

The typical seats.aero/cowtool/etc. user is a "FlyerTalker". We want to go somewhere exotic on a premium airline. If I search SFO-BKK, it's going to require querying basically every one of Aeroplan's partners. AC has no control over TG's backend. AC cannot make it bigger/better/faster.

Maybe AC has to pay Amadeus for those searches. Maybe they have to pay TG. Maybe it's not "dollars", but some other agreement that "if you have 8 million members, you can only hit our system 50,000 times per day".

And here we have thousands of people searching southeast Asia trips with one click, all hitting TG's backend.

AC might be able to handle it. They might even be okay with it. But if TG comes to them and says "you're overloading our system, and it needs to stop or we're cutting you off"... then what. AC did very publicly state that when they tried to launch a calendar[1] they received calls like that from at least one partner.

So even if it's completely legal, would you rather have seats.aero/cowtool, but only half the partner airlines? Or would you rather not have those services, but retain all the partners (with the full availability we were seeing a year ago)? It's not as simple as "AC's backend can't handle it".

That all being said, I don't really like the tactic AC took. Ian said (in this thread) "We attempted to work with Air Canada several times, including offering to change how our scraping worked, but they refused to work with us..."

I tried to talk to them about cowtool for years. I had (well, still have, but it's irrelevant now) a list of questions I wanted to ask them. The very first was "Are you generally okay with it existing?" If they weren't a fan of these things, they could have sent an email. I can't speak for what Ian would have done, but I was willing to acquiesce to their requests, had I ever received any.

They went (over the course of years) from comments like "just because some dude can scrape our site" to "unauthorized systems illegally accessing our site" to (within a week of that comment) sending out a cease and desist. I suspect if they'd just sent Ian an email like "Hey, seats.aero is causing us some issues, can we talk to you about it?" there at least could have been a conversation to see what could be changed.

But AC seems to always take the nuclear option. I didn't know exactly what was coming, but the "unauthorized systems illegally accessing our site" comment certainly led me to believe it was approaching that point.

Also, I still doubt seats.aero is even 10% of their bot problem. I suspect it's substantially less than that. But I'm not convinced they have the ability to determine where the requests are coming from.

[1] AC has also said they have tried very hard to eliminate phantom availability, and when I use other airline's calendars, I find it's very common to click a "70k points" date, and find nothing under 150k. Or vice versa. So I can't speak for how other airlines do it, or if AC could have done a "crappy calendar" that wouldn't have had these problems with their partners.