The difference there is that Banquo and others paying high taxes still contribute more to government coffers than they get in subsidies.

When a political party tries to buy off the poor, then the governments spends much more on those people than it takes in. So, indeed, everyone can be bought, but buying off the poor leads to debt and deficits.

Also, Banquo mentioned a desire to see the inheritance tax reduced because paying it requires selling off assets and firing employees - ie making the less fortunate even less fortunate.

CR