So, in your opinion, a poem is necessarily written within a form?
An inviolate poem is written within purview of {form poetry}. Take any poem that isn't as clear as day prosery, any contemporary free verse and you will find the author adhering to some semblance of traditional English meter and form.
Free verse poetry just means inconsistent meter, not "no semblance of form", "no repetition of traditional poetic technique". Butter's thread is replete with examples of well-done contemporary free verse poetry, OpenField has given us plenty of good examples.
A Sad Thing
byCleardaynow©
Oh. Tis a sad thing,
A sad thing but true.
There is nothing to say
And no one to say it to.
This vignette could possibly be defined within a form: a quatrain, nursery rhyme(abcb)...but no, abcb wouldn't qualify under traditional quatrain rhyme scheme and nursery rhyme is strict on not only stresses, but discrete trochaic units. It is free verse poetry and not prose.