[vkou]

His job isn't to claim that his client is innocent. His to make the government prove the client's guilt beyond a reasonable doubt.

If we don't require that from the government, the entire justice system breaks down.[1] Because once the government stops being rigorous about its methods for convicting guilty people, it can trivially start convicting innocent people.

[1] Which it largely has, given the ratio of criminal convictions that get plead out, as opposed to being litigated. Plea bargains are a blight upon justice.