Stronger:
* Condemn: Express strong disapproval of something.
* Abhor: Feel intense disgust or hatred for something.
* Detest: Feel intense dislike or loathing for something.
* Repudiate: Refuse to acknowledge or accept something.
* Execrate: Curse or denounce something vehemently.
* Abominate: Hate something utterly and completely.
More formal:
* Lament: Express sorrow or regret for something.
* Mourn: Feel or express deep sorrow for someone or something.
* Bemoan: Complain about something in a mournful way.
* Grieve: Feel sorrow or sadness for something.
More neutral:
* Regret: Feel sorry for something.
* Disapprove: Have a negative opinion of something.
* Criticize: Express disapproval of something.
* Dislike: Have a negative feeling towards something.
The best synonym to use will depend on the context of the sentence and the specific emotion you want to convey.