I think that the really interesting question, however is is "how the hell could anyone have possibly thought that saying 'taxation is the same as theft' was a useful contribution to a discussion about the abolition of the 50p tax band, or indeed, anything else?"
If "stealing" means "taking something from someone else without their permission and not intending to give it back" then it is a no-brainer that there are lots and lots of times when "stealing" is very naughty; a few occasions when stealing is very good; and a number of difficult cases about which we can agree to differ. Coming into my house and taking my laptop would be in am example of the first kind of stealing (bad); taking a knife away from a homicidal maniac who was about to stab someone with it, or confiscating heroin from someone who was planning to sell it to small children at the school gate would be in the second kind of stealing (good); stealing bread in order to feed your sister's children would be an example of the third kind (debatable).
Or perhaps you would say: "Ah! But confiscating weapons or drugs, and liberating food to feed characters in long French musicals isn't stealing at all." In which case stealing doesn't mean "taking something from someone else..." It means "taking something you shouldn't have taken". If you go with that definition, then it would be completely untrue to say "Robin Hood stole from the rich to give to the poor". If the rich were really that rich and the poor were really that poor then what Robin Hood did wasn't stealing at all. I believe that this really was the line taken by the medieval English church, in theory if not in practice: it was the rich man's Christian duty to feed the poor; therefore the food didn't really belong to the rich man; therefore it wasn't stealing for the poor man to take it, if he really was starving.
So: "Taxation is theft" comes out as either:
"Taxation is taking something from someone else without his permission. Taking something from someone without his permission might be right or wrong depending on circumstances; so I'll now have to explain what it is about the circumstances of taxation which makes it wrong, which is very much where we started."
or
"Taxation is taking something which you shouldn't take; which is as much as to say, I personally don't approve of or agree with taxation: so I will now have to explain to you why I don't approve of it or agree with it, which also takes us back to where we started."
I suppose it is possible that there could be a rational man who thinks that our society, pretty much uniquely in the history of the world, could get by without a system of taxation. (Is the idea that the police will send you a bill after they catch, or more likely don't catch, the guy who stole your laptop and gave the proceeds to the poor? Or that once we all have guns, we'll be able to defend our own houses and won't need policemen? Will there be people who can't leave there own homes because they can't afford the toll to walk on the pavement? Or what?) But "I don't believe in taxes because taxes are a form of theft" is a meaningless sentence, boiling down to "I don't believe in taxes because I don't believe in taxes."
See also "I don't believe in hanging / war / smacking foxes / hunting children because hanging / war / smacking foxes / hunting children is a form of murder / violence / not the sort of thing which is acceptable in a civilised society."
I find this kind of thing keeps happening to me. I think that it is quite possible that I am in fact the wisest man in Athens, or a corrupter of the nation's youth or something.