So when i find a really nice piece of software that actually saved me a lot of money (by increasing productivity and reducing licensing cost of other dev tools), i don't mind paying them a 70$ one time fee.
Because in the end, they are not going to pay their employees with your respect.
So, you have all the right not to pay them, you also have the right to leave shitty tips all the time and to not go voting.
But i think i don't need to explain what will happen if we all act like that.
The key words there are "for the evaluation". As soon as you're using the product for real, you are required to pay for it.
Screwing them over? Ridiculous. They've explicitly given me permission to not pay them!
No, they have given you permission not to pay them while you evaluate the product. After that, you are explicitly required to pay them if you want to use it for real work.
It's free to evaluate for as long as you'd like. Once you start seriously using it, and making money with it, you need to buy it.
You're breaking the law? No, you're not. On the download page it explicitly says "There is currently no enforced time limit for the evaluation."
Screwing them over? Ridiculous. They've explicitly given me permission to not pay them! I'd be doing them a favor if I paid them. I would be showing them a lot of respect. That is a good thing, but it is not inherently bad to accept their charity and use the software freely.
As far as I can tell, it's a clever business strategy for disseminating free software, with the hope that people will purchase it out of respect for the art. It's a clever business move because it gets the software out there in mass so that it becomes popular.
They shouldn't expect everyone to buy the software when they explicitly say they don't define a time limit in which one has to pay. I would bet that they even don't expect this.