But it's quite another thing if someone tries to convince you to behave one way while s/he secretly behaves differently- and it is to his/her personal benefit and (perhaps) to your detriment to do so.
For example, if somebody makes a 'moral' claim that all feezos should be in the public domain in order to convince others to donate their efforts, but that person makes a best-in-class feezo based on all the others' work and doesn't release it into the public domain, that person is a hypocrite with bad motivation. I don't like those people. I don't excuse those people. Any public good that comes of it is likely accidental, although I am sure they will try to convince you otherwise.
So I agree with sbov with the following addition: I don't care about the hypocrite's arguments of persuasion. I won't throw out a good idea just because it comes from a hypocrite. But I won't believe it's a good idea just because the hypocrite says so even if the hypocrite is an expert in the area being discussed. I will seek other ways to validate his claim. And yes, I know, we should always do this, so I can state this a different way: I won't use the hypocrite to validate a claim.