Mark,
I find a poem like "If--" to be mediocre at best. It's meter is so perfect it puts me to sleep, and I've never come back to it and found something deeper or more interesting. Similarly, from the American list, 'O Captain My Captain' is such a bore to me (and I like Whitman).
Anyway, we're talking past each other in one sense: these poems here are 'universally loved' (and here we're seeing that's still not true) by the subset of poetry readers, right? That's, sadly, a small subset. My glib comment sets up a "No True Scotsman" of sorts because in my sense a "universally popular poem" would have to be way more expansive than anyone could prove (i.e. ask my sophomores [or Year 11] what they think of 'To Autumn'). Such a broad expectation of popularity to prove worthless in a real discussion.
Let me end on agreement: there are many beloved poems that are justifiably beloved, even if I think "If--" rubbish and think it takes until #6 to get to a great poem that is the work of a great poet (Tennyson and Wordsworth are great, but those aren't their best works; Smith is a very good poet, but I don't know her well enough to call her great, nor do I love that poem).
To paraphrase Oscar Wilde's lovely line 'There is no such thing as a moral or an immoral book.
Books are well written, or badly written. That is all.” I would say say the same about poems and the value we place on their 'obscurity'. They are either good poems or bad poems. That is all.
I agree with this sentiment wholeheartedly. Though, for my taste, the best poems are the ones that reward re-reading. What makes re-reading worthwhile? Seeing new things, which, for me, usually means a density (in a loose sense) of form and content. That often means finishing a poem and not "knowing what it means" because it can sustain multiple meanings. Like Keats said about what he called Shakespeare's "negative capability": "being in uncertainties, mysteries, doubts, without any irritable reaching after fact and reason." 'Prufrock' appears on the American list, and it's a hard poem, but one that is (to me) beautiful even when you don't know what's happening. It rewards re-reading--I teach it every year and find something new and interesting I never thought of.