Tipping culture is criminal - particularly in the US where it's so ingrained. I don't understand how some industries expect it, whilst in others it's non-existent (there's plenty of other lower paid jobs where tipping doesn't occur). We need to move away from it as a society, and encourage employers to pay their staff the living wage. Especially when - like others say - they themselves are earning mega money.
That said, I think it should be at your discretion. If you have good service, then a €1 or 2 extra isn't going to make a great deal of difference, and it will get you served quicker on repeat visits. Anybody who asks for it, doesn't get it - that's how it works for me. It's a privilege, not a right (unless you're in the US!)
There have been instances where bartenders have taken it without asking in the past. Not on. If you want to swerve this, pay by card and keep some change to tip in addition, should you so wish.
We've all been talking about how expensive the island is - you shouldn't feel pressured into spending any more money, particularly for sub par service.