The “value” of existence is not subjective. The final cause of any living thing is to preserve its own life (and pathological cases, such as a person who is clinically depressed, are not counterexamples to this - they are just instances of less than perfect instantiation of the form of a human being, in the same way that any triangle you draw on a sheet of paper will be a less than perfect instantiation of triangularity).
I appreciate this difference in orientation. Where I think both sides can agree – the Thomist and the secular modern philosopher – is that it makes no sense for something to have “value” without a consciousness and intentionality that does the valuing. Money, for example, has no inherent value. Gold has no inherent value. A string of yarn that reminds one of one’s grandmother – who used to knit winter hats and scarves when one was a child – may have no value to others, but to oneself it could be among the most valuable things in one’s possession.
Money has value – and the words of our English language have the meanings they do – because of an inter-subjective consensus that, in a sense, become “objective.” It is an objective fact that $100 has more purchasing power than $1, precisely because the value one ascribes to each is not subjective but
inter-subjective; there is consensus.
The desire for life (as opposed to death), for liberty (as opposed to enslavement), and for happiness (as opposed to misery) is indeed universal, in the sense that it is inter-subjective. In this limited sense, it is thus indeed
objectively true that life, liberty, and happiness are inherent values.
The extra step that I think the Thomist needs to take – to get from subjective, to inter-subjective and universal, to truly
objective (in other words, not dependent on human subjectivity) – is to say that the conscioussness of
God values existence, which is why we cannot help but value existence as his creatures. God’s subjectivity, as it were, defines what is objectively true (as opposed to human subjectivity or even human inter-subjectivity).
If one is not convinced of God, saying that evolution – for instance – is the
only reason why all creatures generally seek to preserve their existences and to avoid undue suffering, then there can be no objective value to existence (which theists themselves point out, when non-theists argue that an “evidential” objective morality still exists, in the absence of God, based on the universal preferences of humans and of other creatures). There needs to be a consciousness that does the valuing, and that consciousness would need to be God; otherwise, in a material world that is not conscious, there can be no such thing as inherent value (in this respect, I stand by my position that “value” is an intentionality-word, akin to saying, “I like this, I like this very, very much; this is important to me; I
want this. This is good – not even in a moral sense, but in a
pleasure sense. This is inherently pleasurable, worth striving for”).