I would strongly disagree with that...
A poem of course should adhere to basic principles but it doesn't have to be geometric, it doesn't have to be logical, it can be weightless, airy, incandescent and free form.
Mathematics can kill poetry, confine it in a rigid cage of measures and feet, and metre. The natural result of such strict over adherence to supposed poetic principles was the Augustan period of elegant but stale, practised poetry in the 18th century that the later romantics strove so hard to break free from.
There's a difference between analytical examination of a poem and over-egging the pudding.
What's wrong with a little sentimentality anyway?
I would argue that a love letter or poem written in the heat of the moment will invariably convey to the reader a far more visceral and genuine emotion than some cool, calculated, carefully selected verse.
Many may disagree of course, my own poetry I know well enough is very rough and unrevised, mostly spontaneous and overly sentimental but that's my own method [or lack thereof].
Rant over

"Oh what a misery it is to have an intellect in splints".