There is a saying: One who cannot curse cannot cure. “Cursing” is often a matter of perspective. The cancer cells invading my friend’s body probably weren’t that happy when 200 witches started blasting them, but when my friend went into remission we didn’t think much about how many death curses we had delivered to those cells.
A banishment is a type of curse, and I’ve delivered plenty of those. Justice work can involve cursing, and so can reversals. My own High Priestess “cursed” me with “students that ask as many difficult questions as you do”. (Coming on here keeps me sharp, but Quora’s got nothing on what my covenors throw at me.)
So, while others may differ, I would say it’s very possible for a Wiccan to curse. The three-fold paradigm and the rede say to me “clean up your own mess”. Sometimes, that means getting a little dirty.