The difference is that Max and Tanya have other storylines, not just ones where they'e kissing etc. Christian and Syed kiss in nearly every scene, Christian is only in Eastenders as a token gay character.
When was the last time we saw scenes like that involving a straight couple? I'd say the gay characters get far more kissing scenes than is necessary just because they're gay and Eastenders wants to be seen as "trendy and PC".
As for two men kissing being "sweet" well I think it's about as sweet as a mouthful of raw liver and equally as disgusting at that time of night. Two women kissing is the same and as far as anyone snogging goes I don't really want to see it whether they're straight, gay or bi.
Edit: I don't think it's okay to show any graphic sex scenes in a soap, we should be left to just assume what has happened. Eastenders is pushing the boundaries too far and it won't be long before it loses even more of it's viewers.
The reason that so many people are against the gay scenes is because Christian is such a pointless character, only in it to be gay. There's nothing wrong with having gay scenes in a soap as long as it's part of a good story but Eastenders seems to show them snogging for the sake of it, there's no need.