your argument boils down to "it is convenient for me, and I see other people stealing bags too".
1. It is straightforward to restrict a DNS server so that it only answers specific networks. This doesn't even need to be close to comprehensive to get the message across. Level 3's (née BBN's) intent is to continue to respond to the wider Internet community, regardless of what their ambient PR says. Likely for similar reasons that they run a looking glass.
2. The frequency and magnitude of your scenario makes it a straw man. A more worthwhile example is someone using a business's bathroom without buying anything. Yet most places don't really care as in the end it balances out, and we're all humans that have needs that can't be fully met by commercial provisions. The major concern is people who mess up the bathroom, paying or not.
3. While a common touchstone, theft does not apply has nothing has been taken. Perhaps unjust enrichment. But given that anybody using 184.108.40.206 to answer production DNS queries is actually harming themselves with additional latency more than anything "taken" from Level3, that's a stretch too.
Have we really become so full of corporate bullshit that we're stuck analyzing things in its myopic paradigm? I thought this was Hacker News?
PS I notice 220.127.116.11 also responds to pings and DNS queries. Should I expect to get a bill for their services? Because I'd much rather just relish the feeling of a fleeting shared purpose with someone halfway around the world in a vastly different culture.