According to "snake standards"? Has a group of snakes convened to agree on a quality of life index? And if so, how has this person been informed of it? Do they speak snake?
If I have learned anything in the short time that I have been keeping snakes, it is that they are simple creatures without the burden of complex, socially mediated thoughts and feelings. It's something I like about them. Given adequate space, food, water, hides and temperature gradients, I doubt they feel like they need to complain about anything. Nor do they probably have any concept of what life in the wild is like or how it would compare to life in the viv. People feel miserable when they can imagine how life might be different. I don't think snakes have a point of comparison, but can simply perceive whether or not their needs are met and based on that, whether or not they are suffering.
Suggesting that a snake is miserable in captivity is anthropomorphizing. While I don't think snakes are stupid creatures that function entirely on pre-programmed instincts (they learn and remember things), I highly doubt they even understand the concept of captivity or possess the intellectual capacity to compare captivity to anything else. An enriching and healthy environment can be easily created for snakes in captivity and I am sure that as long as snakes do not feel cramped/sick/exposed/the wrong temperature, they are content. Snakes like places that make them feel secure and my snakes voluntarily return to their own vivs when they're tired of being handled; it's familiar and comfortable territory to them. I don't think snakes make escape attempts for the sake of some idea of freedom. My snakes only get restless when something about the viv environment is not meeting a need -- hides aren't good enough, the tank space has been outgrown, the snake is hungry. Once the issues are corrected, the escape behavior stops.
Personally, I would explain to this person that they are anthropomorphizing, but if they refuse to listen to reason and are instead wrapped up in their own feelings about this issue, there's not much to be done.
On a not totally related note, I do sometimes think about my disconnect from nature when I look at my vivs. Living in the city, it's like I unconsciously need to put some of nature in a glass box so that I don't feel so separated from it.
