My instinct is very much to say no. You wouldn't like it if I cancelled your credit cards to save you from yourself and many people would see magic without consent as a similar type of imposition on a person.
But like most witches I frequently practise the very opposite of what I preach. Its tricky because sometimes a witch will find herself in a position where she may not wish to reveal to a person that she actually is a witch, so completing the magic in secret can seem the better option. I also practise magic where it would not be appropriate to tell a person what I am doing. This could be because I need them to be unaware of the spell I am casting. I recently cast a changing mind spell on another person for my own ends (worked like a charm!). Asking that person if I could cast a spell on her in order to change her mind would have rendered my magic futile.
However, an older and considerably wiser witch than myself believes absolutely in the necessity of consent. She gives
the example of secretly curing somebody of common cold symptoms. On the surface it looks a pretty harmless thing to do but she argues that firstly by removing the symptoms it may make a more serious health problem go undetected and secondly that person may need that cold to legtimately rest for a while. We do not know if three days off work would be spiritually beneficial to the individual and who are we to deny them that recourse? As we cannot fully know a person's full circumstances without their knowledge, her argument would be that we are not in a position to ethically use magic without discussing it with the person involved.
So there are very definite pitfalls involved in magic without consent and in answer to your question it would certainly go against the ethics of some witches. But speaking personally I do not believe it is possible to be a practitioner of magic in a world where consent is always needed, so yes the concept in principle does go against my ethics, but no I won't stop doing it!
Image ID: 10014514 renjith krishnan. Free digital photos.net