They call it "theft" for the defensible reason that it maps to traditional theft in (what they regard as) the most important dimensions. Your disagreement with the validity of the (IMHO, obvious) mapping doesn't make it lazy.

Theft is wrong for well-known reasons. Most of those same reasons apply to these situations.

> Sitting in an airport lounge you shouldn't have access to isn't stealing.

What do you think of random people occupying your house while you are gone out to work or grocery store? Is that okay too?

> Using ad blockers on a site that supports itself through ads isn't stealing.

I agree with this because browsers are "user agents" not "website agents".

Airport lounges offer all kinds of drinks and snacks that I'm certain this person is not ignoring. They are also using the facilities and causing more congestion, making it less pleasant for the paying customers, so they are stealing the value that the lounge offers from other customers.

It may be classed as theft of services.

If curious, consult a qualified legal representative in the appropriate jurisdiction.

What about the food and drink that are offered in these lounges?

You may have a point.

So opposing trespass is now rooting for corporations?

Well, @eunoia seems to think so. I happen to disagree. But at least now we can discuss it without the emotional baggage of calling someone a thief. For whatever reason, people get worked up over that label more than "trespasser" or "squatter" or "moocher" ;)

I'm afraid we all might be wrong/right on some level. I.e.:

1. Getting into an area you don't have access to: Trespassing.

2. Tricking the security they have in place: Fraud.

3. Taking snacks from the lounge-area: Stealing.

> Sitting in an airport lounge you shouldn't have access to isn't stealing

You are consuming a resource that's finite. You are literally taking value from the provider without asking or paying for it. What do you propose we call this?

Physical space in a building is a limited resource. "IP" isn't.