Whether you agree with it or not the Financial Transaction Tax boils down to one thing. An unlected government (the EU) taking money from one group of people and spending it in a way they see fit.
In short the EU believes they can spend the money in a better way than the people who are being taxed.
To my knowledge, there is no evidence that the EU has the ability to spend this money wisely, given that the EU is blaming itself for the Euro crisis because they did not implement it properly.
The EU has declared that taxes are designed to cut the number of people doing something that the EU sees as undesirable.
An effective curb on automated high-frequency trading and highly leveraged derivatives
Whether you think it high frequency trading is good or not is besides the point. The point here is whether people in Europe are happy to accept unelected politicians judging for them as to what is acceptable behaviour or not.