The reason why we're so against it is the implications of getting those wings. She is now ridiculously close to reaching goddess or demi-goddess level in terms of power. Also, alicorns can live over Millennia, so if Twilight can truly harness the true power of becoming an alicorn, she can essentially outlive her friends. Finally, was it ever hinted in the slightest that she wanted to be an alicorn over the past 3 seasons? NOPE. And at the end, she accepts it point-blank which seems flagrantly out-of-character for her. It seems like McCarthy wanted to ruin Twilight's character development in favour of making her a Canon Sue.