What I Don't Understand

I understand that Roger Clemens lied to Congress. I understand that that is a very serious charge. After all, if witnesses are allowed to stand before a Congressional panel and say what ever they want, without any regard to the truth, then there is no point in Congress having investigative powers at all. I understand that young athletes want to emulate famous stars, and that when what they use steroids to be like Roger, it can kill them. I understand that is appropriate to charge Roger Clemens with lying to Congress, and if found guilty, it is also appropriate to send him to jail.
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What I don't understand is how tobacco company CEOs can come before a Congressional panel, swear to tell the truth, and then state that tobacco is not addictive, and not be charged with lying to Congress, just like Clemens.