GPLv3 says that
nothing other than this License grants you permission to propagate or modify any covered work. These actions infringe copyright if you do not accept this License. Therefore, by modifying or propagating a covered work, you indicate your acceptance of this License to do so.
I know that you're asking about other (weak) copyleft licences, but the text above is so clear, and the point so general, that I thought it worth quoting. If you are only permitted to reproduce someone else's work if certain conditions are met, and you fail to meet them, then you have no right to reproduce their work, and if you do so you're infringing their copyright. The Apache 2.0 licence includes the grant that
You may reproduce and distribute copies of the
Work or Derivative Works thereof in any medium, with or without
modifications, and in Source or Object form, provided that You
meet the following conditions:
(c) You must retain, in the Source form of any Derivative Works
that You distribute, all copyright, patent, trademark, and
attribution notices from the Source form of the Work,
excluding those notices that do not pertain to any part of
the Derivative Works
So it's pretty simple. By removing others' copyright notices you fail to meet that condition, and by then redistributing their work (in source, object, or binary forms) you're committing copyright infringement. Depending on the jurisdiction you're in, legal remedies for that include injunctive relief (where a court orders you to eg stop distributing your derivative work, and/or to recall and destroy any copies already distributed), compensatory damages (where a court estimates how much money the plaintiff would have made if you'd had to buy licences for the work you copied, and makes you give it to him/her), punitive damages (where a court makes a public example of you by giving a lot of your money to the plaintiff), and may include other remedies. In some jurisdictions imprisonment is a possibility.
Evidence that the infringement was deliberate (your part two above) may make certain of these penalties more likely to be applied, but it will all depend on local law (and you don't tell us your jurisdiction), and in any case IANAL/IANYL.
It's crazy to risk that. Free software gives you so much for little in return: just honour the licences and all will be well.