Oronte truly is a man of his age, because his poetry has distilled all that Alceste hates about society into a convenient, readable package. It practically gives Alceste a heart attack. After begging Oronte not to read it, he finally spits out, "This artificial style, that's all the fashion,/ Has neither taste, nor honesty, nor passion;/ It's nothing but a sort of wordy play,/ And nature never spoke in such a way" (1.2.148).
Remember that Alceste is Mr. Sincerity, so he hates anything that seems artificial. Just like Philinte hugging those guys that he can't even remember, Oronte's love poem has no emotion in it. Everything about it is fake, fake, fake.
Let's check it out:
Hope comforts us awhile, 'tis true,
Lulling our cares with careless laughter,
And yet such joy is full of rue,
My Phyllis, if nothing follows after.
Your fair face smiled on me awhile,
But was it kindness so to enchant me?
'Twould have been fairer not to smile,
If hope was all you meant to grant me.
If it's to be my passion's fate
Thus everlastingly to wait,
Then death will come to set me free:
For death is fairer than the fair;
Phyllis, to hope is to despair
When one must hope eternally. (1.2.65)
Didn't that make you swoon? Wasn't it full of emotion and passion?
Yeah, not us, either. In fact, it kind of reminds us of those Valentine's Day cards we got in elementary school. You know, the ones with the gross chalky candy.
So, it's lacking in emotion. It's bad. To Alceste, it's a symbol of everything that's wrong in the world.