Taking what people think lightly is a skill practiced by all politicians. They are very good at it.
Because harvesting email addresses is pretty much the ultimate purpose of all online petitions.
Which part excludes it?
Use of government resources for an election campaing is another issue, one more than just privacy activists care about.
In a world where the President can take Air Force One to go to a campaign fundraiser, I don't think that this is taken all that seriously any more. There are certain rules regarding what's "politics" and what's "government", but if the White House has your email address you're certainly gonna be getting a lot of emails going "Gosh, what a good job I'm doing as President. What a pity those darn Republicans are to blame for everything that's going wrong" et cetera.
Says who? I've been registered on more than one petition websites for years using an email just for them ([name-of-site]@mydomain.com) and I haven't ever got a spam email.
Do you have an evidence of this ever happening, or are you just defaming?