A massive question that is asked in many of the poems of Tennyson is about the value of life and in particular whether it is better for people to live pale imitations of life, even though they are trapped from truly living, or to live truly, even though if that act of living will surely bring them death. This seems to relate to the ethical question of what kind of value do our lives have and is it fair for humans to have a "life" that isn't really a life in any way at all. Note for example how this is explored in "The Lady of Shallot," which is one of many poems by Tennyson where a character is trapped away from society by "four grey walls and four grey towers" on an island, and is only able to see the world through the reflection that is shown on her mirror. It is when the Lady of Shallot sees the young, virile and handsome Sir Launcelot that she decides to look upon life and truly live, even though she knows it spells her doom. The same themes of entrapment can be seen in various other poems such as "The Sleeping Beauty" and "The Kraken." Note, for example, the final two lines of "The Sleeping Beauty":
She sleeps, nor dreams, but ever dwells
A perfect form in perfect rest.
Such lines beg the question that if this is a "perfect form," what value is her life is she is unable to participate in it? An excellent thesis that could be used to explore this ethical issue would therefore be:
The characters in Tennyson's poems are unable to participate in life and are only able to live half-lives, which shows that any life, even a short or tragic one, is better than a life that is not really a life at all.
This would allow the exploration of various other characters Tennyson presents, such as Mariana, in the exploration of this ethical issue.