I have no problem with tipping extra, when someone does extra for you. Dannyboy's post is a good example of that.
If the cabin steward cleans the room twice a day, leaves clean towels and fills the ice bucket (I guess that's now "extra" on Carnival) I don't tip extra. If I want an extra chair for the balcony, extra towels each day, extra glassware..etc. and they do it, then I tip extra.
I have tipped room service, on cruise ships, since I first started cruising. I've worked the service side of the hotel and restaurant business and I believe some body carrying a tray of food and plates up a number of decks and delivering it to the room is worth a couple of bucks. Especially since there is no charge for the food.
Hotel room service is the rip-off. You pay a higher cost for the food, they add a 18%, or more, service charge and then expect a tip. Now, that's a rip off and one that I hope cruise lines do not follow.
I have always left a tip for the cleaning people at hotels. I know people who are cleaning staff at hotels and they work their "butts" off and are treated like dirt by most people. You would not believe some of the literal "crap" they have to clean up.
I never tip for a bad job or when someone does not deliver. I rarely pre-tip unless I have a number of specific requests.
Over the years I've read the postings of people who slip a $20 - $50 or $100 to the cabin steward when they first meet them and then brag about how great their service was. Well, I didn't and I still got great service. A lot of pre-tipping is stroking the ego of the person giving the tip and not for the benefit of service or the staff member. Some people like to feel like a big shot and, if they do, that's fine. It's their money and if it makes them feel good then go for it but don't expect everyone else to.
Tipping is a personal thing and it's up to you how you want to do it. The thing I do have an issue with are people removing their gratuities from their account for no reason other than they don't believe in tipping. Well, that is also their decision but they are still cheap. Write a nasty letter to the President of the cruise line, post your displeasure of tipping on every board but don't take the salary away from the person who is going to be working, very hard, for you. BTW: They know if you removed your gratuities.