I don't see the problem. If you take a step back, you'll see that a lot of tennis fans have picked their favourite, and have a fixed idea about who should be allowed to beat them, so see everything through that filter.
The timing of Murray's rise meant that a lot of people had latched onto other players who are still active, so in their eyes, he's always going to be the challenger, so need to explain away his success. They are also more likely to latch onto behaviour as an excuse to hate that wouldn't bother them in their favourite or someone who isn't a threat. By the time they've bumped their gums a bit, more neutral people can be influenced.
In Andy's case, the whole saga of him being "anti-English" was taken frighteningly seriously by people who would claim to never pick up a tabloid, never mind read it. It's just one of those stories that grows arms and legs and becomes an established "fact".
An actual well established fact that once someone has decided that they like, or don't like someone, they'll selectively notice and believe positive, or negative reports or press about them.
But if you were a fan of another player, you'd see plenty of hate going in their direction, often just as unjustified.
To be honest, I don't think it's worth worrying about what the more mouthy people on an internet forum have to say. This kind of place attracts people who want to moan or demean people who have achieved more than they could dream of. It's the nature of the beast.
I also think that a lot of people who make wild claims are doing so with their tongues firmly planted in one cheek. All the stuff about the wind - most people are joking.