Lowering Corporate taxes helps them propel forward, to dump their money into increased productivity, to be more competitive, which could mean hiring more workers, increasing research funding, building new facilities etc.
How is that bad?
It would be great if that's what happens, but it just doesn't happen. It didn't happen when Reagan cut taxes, and it didn't happen when Bush cut taxes.
Any increase in jobs which came about after both of these tax cuts can be directly attributed to the massive increase in government spending that both men made after cutting taxes.
Reagan went on a military spending spree which doubled the deficit and then tripled it. The American Military Industrial Complex made out like bandits, and thousands of jobs created at places like Boeing, and other corporations whose primary customer is the US government. These are technically called "private sector jobs", and thus count as "new job creation", but these jobs would not exist if not for government spending.
In Bush's case, the government spending was on wars abroad which was even more detrimental to the US economy. The money was spent OUTSIDE the US. Massive amounts of government money provided limited economic stimulus in the US. At least Reagan's military spending stayed at home.
When his voodoo economics failed to deliver the jobs promised, unemployment hit 6%, and the deficit which was supposed to be paid for by growth, tripled, Reagan went on a government hiring spree because government workers pay mortgages and buy cars too. He also raised taxes too which shows that some people really do learn from their mistakes. Too bad the rest of the Republican Party skipped school that day.