I'm not encouraging that anyone steal anything. I still do see milk crates in a hefty abundance, and many times they are most obviously left for dead. I am in a busy city, however, and realize that this is not the case for everyone...
I am the type that will always flesh out my options before laying down money, and I simply wanted to point out that milk crates are an item that tend to be floating around out there saturating the nooks and crannies and if you bother to snoop, you'll likely be rewarded. I'm sure countless people on HBT use plastic buckets that they've either found on a curb, or acquired by speaking with shop/restaurant owners, and I believe those innovative efforts are applauded rather than shunned. One less piece of plastic waste.
Also, I believe both that there is a time for encouraging theft, and that theft is a very peculiar concept, subject to a range of interpretations. While yours may be rigid and fixed in place, mine accepts that nothing is cast in stone.