Ugh... I guess someone has to explain this to the kids who never took eco100.
Ok, taxes are a disincentive to act. Why? Because, when you take that action, you are "taxed". This isn't to say that taxes are bad or wrong, they are not, and a well designed and fair system will benefit everyone (although not equally).
So, what you need to consider is what behaviours you want to promote, and which behaviours you want to demote. So, let's start with the second part - the behaviours we want to discourage. This is why we heavily tax things like cigarettes and alcohol, because we recognize that as a behaviour they are costly to the system (from health costs, and policing costs, etc). Same with fuel consumption taxes on automobiles. If your car is less efficient (say a big-block v8 HEMI) we are going to tax you on that purchase more than if you paid the same amount for a fuel efficient hybrid.
Ok, now the hard part - what behaviours to we want to encourage? Well, let's start with the easiest one - inheritance tax. Everyone is going to die at some point, so we as a society have decided that once you are dead, there is no tax to be paid to your heirs. This seems to make sense as we want to encourage families to pass wealth on to their heirs. It seems a little unfair to work your whole life to acquire assets and then have the government take an extra chunk at the end... but some countries do this the U.S. for one.
Now, the final consideration - income taxes. Why do we tax labour differently than passive sources of income (capital gains and dividends)... and the answer is that it is an incentive to put capital back to work into the economy. IF we treated all sources of income the same, then as an individual you wouldn't care if you saved, or invested or spent your after-tax income. As such, there would be an increased incentive for people to simply "buy stuff"... this would decrease the pool of money available to entrepreneurs to start businesses.
For those of you confused at this point - let's take a very simple example. Take, Dragon's Den on TV. As a person with a new business idea, you need capital to make the idea happen, so you make a pitch to investors. The hidden part of the show (or any investment) is the tax break on the successful investment. Thus, if we taxed everything the same, then an investment into a new business would have to be TWICE as attractive as today, to attract the same investment (as today taxes are half for investment gains).
So, if deals need to be twice as good, obviously, less deals will get done. Now, magnify that across the entire economy and you have significantly less new business going on. Since most businesses in Canada are small businesses (less than 50 employees) it's going to hurt.
So, TL:DR- it isn't really about saving the rich, as much as it is giving an incentive to behaviour we want to encourage (new investment).