So there I was, getting into the swing of Wikipedia, doing my bit for (among others) numerous entries relating to Buffy. I noticed that the pages for Darla, Angel, Spike and Harmony repeated a bunch, so I created an entry on Joss Whedon’s vampires to collect it in one place. Six days later someone else came along and replaced it with a much longer article full of misspellings and clutter, retaining not one of my well-written sentences.
Harrumph.
I guess every contributor gets a similar shock sooner or later.
The trick in such circumstances is to figure out who did the edit and gently discuss with them the need for better grammar, spelling, etc. The user’s talk page is designed for this.