I would argue that shaping behaviour is another aspect of looking after your key supporters. If you put taxes on speculative trading, such traders won't vote f

I would argue that shaping behaviour is another aspect of looking after your key supporters. If you put taxes on speculative trading, such traders won't vote for you -- but people who are against speculative trading will. If you give speculative traders a tax cut, the inverse happens. It also obviously will shape behaviour, but if that was the only purpose then the government wouldn't be fulfilling their primary purpose: trying to stay in power as long as possible so they can achieve whatever they set out to do.