But anyway, I do not know if we can equate "sentience" with "purposeful behaviour".
At least not in the sense that a sentient human being devotes all it's capacity towards a single purpose. I think that the base of knowledge and understanding required to achieve such a thing is rare among us.
A person who strives to reach a goal does so with purpose, but no one can control every variable in one's life, so things are bound to happen by accident, even if these accidents serve to fulfill the initial purpose.
For myself, I see no moral or ethical objections to the creation of simple living cells. There are a few issues that at first seem moral, but if I am honest with myself I realize that these objections are founded in the instinct of self preservation.
For example, should we create that which potentially can become a contester for our dominace of this planet? (A.I. or lifeforms that have a superior potential to humans).
A single cell isn't likely to be this threat to us, but it could well be a first step towards the coming of something that we didn't intend, or the breeding ground of some "accident" that we didn't forsee and that can become a threat to our very existence.
But I do not think these are moral considerations. More a fear of evolution passing us by, in a manner of speaking.
So it would seem. That should teach me not to reply to posts when I'm crosseyed from reading too much fiction 
