Same here on every count. It's free money and free protection.
The only argument I can see against was posted on another thread over the weekend.
Essentially by taking advantage of the offers and paying nothing to the credit card company my use of cards is potentially being subsidised by the more vulnerable members of society who are paying the high interest rates and penalties - those potentially that are in the least capable position to afford it.
That is a possible moral argument against using them - but the same argument could be used around many things, for example I seek the cheapest gas/electric rate I can but I know that people who are potentially vulnerable may be being gouged on pre-payment meters.
People with poor credit will also get higher interest rates - unfortunately it is the way the industry works in that the people with least money tend to end up paying more for many things because they are higher risk for maintaining payments.