Well for one, taxes feed into things like infrastructure and the social safety net, which because of the way the government works, is in a lot of cases what's keeping poor people alive. For two, lower taxes on corporations doesn't affect all that much what the average employee makes—it affects the profit margin and how much the executives are getting. This does have some effect on the economy, but the argument from this point of view, which seems to bear out historically, is that the economy on the whole does better when regulated to a certain degree than when corporations are allowed maximally free rein.