to be fair, QM, it's almost certainly ignorance rather than laziness; people just don't know the difference, because they sound identical. Serendipity, 'have' is what is called an auxiliary verb - it helps out with other verbs. I have done it, I would have done it, I could have done it. But they are seldom pronounced that way; I have done it is often shortened to I've done it, and would have and could have are almost invariably shortened to would've and could've (and should've) as QM says.