Because if we start punishing people for what they say, unless it's liable or a threat against someone's life, that is a sign of unamerican values take precedence in a vengeance based witch-hunt.
So for starters, there were actual intrusions into voter databases. There is no evidence that anything was changed (and probably significant evidence that nothing was changed), but the fact remains that the Russians made illegal intrusions into our voting systems.
Also, I would argue that illegal foreign propaganda is not protected under the first amendment, since many of the claims made by spam-bots are essentially libelous. The first amendment exists as a protection for US residents to express their gripes against the government, not for foreign entities to spread propaganda that shifts American sensibilities towards unstable, extremist ideologues. Note that the law agrees with me on this: if Annoying Orange (or any candidate for that matter) were shown to have colluded with a foreign entity to spread propaganda against their political opponents, that is basically a textbook example of high treason.
Ask yourself this: if North Korea started a massive email spam campaign against US citizens talking about the evils of our government and the superiority of the Kim regime, would your first reaction be to thank them for their free speech, or to sanction them for exploiting computer systems to spread propaganda?
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