I happen to think that the founder of Snopes embezzling $98K and spending it on prostitutes is relevant, as it throws their entire journalistic credibility into question.
So the founder of Snopes may be financially dishonest and driven by sex thrills...but this doesn't invalidate their research on external questions. It's not like I looked to them for moral guidance about, well, anything.
I'll worry about that if/when it happens. I have no difficulty distinguishing between factual and editorial content, and I generally only consult Snopes after I've done some research of my own and drawn a preliminary conclusion.
On the surface, your argument is correct; the facts are the facts, and no amount of moral corruption will change that. Things get hairy when you remember that our world is anything other than black and white: facts can be distorted, misrepresented or ignored to deliver an entirely different message, even if they are still (technically) "factual".
This is why you don't want a known sleazebag for a reporter. Not only do they have a provably skewed moral compass that would let them deviate from pure "fact-based" reporting, there is also a safe assumption that they have other, worse skeletons in their closet which would mean they're susceptible to being blackmailed into deviating from pure "fact-based" reporting.
Communicating in a large internet forum is quite different than in small groups or in person. Among other things, it's much harder to communicate intent, so it's best to either (a) state intent explicitly or (b) edit the post so that it isn't so vulnerable to crossed signals.
For any other reputable news source I'd totally agree - but in this case, it's poor form to give the Daily Mail your ad revenue. This is not any regular newspaper: it is a mouthpiece for an organised hate campaign aimed at stirring up political tensions against immigrants, the disabled and out of work, and other 'undesirables' - which just also happens to be really good at writing social-media-friendly celebrity stories.
The reasons you gave don't rise to that level.
If the other critique I made—that they don't actually mention anything wrong with the mail article— wouldn't be the case, it wouldn't be as bad.
But the fact that they didn't make any substantive critiques of the article and didn't link it makes it a hit piece.
I think "I want to talk about their attitude to fake news, not further spread the salacious details of their only-sort-of-related coverage" is ... a reason.
I think saying basically that, and providing a link afterwards that one would hope readers would choose not to click, would've been a better approach from a broadsheet.
The guardian article is a hit piece, and a poorly written one at that. It gives very little information and a lot of vague or indirect criticism. (Makes you think how much more effective hit pieces can be when the writer actually has something to work with: even this will probably convince a lot of people that critiques of snopes are invalid.)
On priors I'd expect there to be issues with the mail article, but the guardian doesn't tell me what they are.