People denied it because they have a different opinion to you, not because they are ignorant or have an inferior understanding of a topic to you. You accused people of 'casual racism' based on incredibly flimsy evidence, and are now accusing people of ignorance and 'showing a lack of understanding' because they take a different position on what should actually be considered racism. I'm not surprised there was a melee, it's not very nice to be accused of being casually racist because you called a player lazy or overweight, the same way people accuse Fellaini of being a donkey or Phil Jones of being the thickest player to grace the game. You're placing insidious intent on harmless comments reflecting frustrating at a player who is performing poorly, and you're then surprised when they react badly to that? Your opinion is that it qualifies as casual racism. Other people's opinion is that it qualifies as the same kind of abuse that other members of the team receive.
Of course stereotypes exist, and I don't think many on this forum would argue that racism has been taken out of the game or deny the existence of stereotypes. There is still certainly a tendency to pigeon hole black players and you see plenty of lazy generalisations across the internet, but that doesn't mean that Lukaku has been the target of casual racism on this board. Your argument is what, because in the past black players have been stereotyped as lazy & lacking in intelligence, people who are now suggesting Lukaku is lazy or lacks intelligence are automatically doing so because of the colour of his skin? What happened to approaching situations on a case by case basis, instead of horrendous group think identity politics in which context becomes nothing more than a hazy blur?
Lukaku has appeared lazy this season. His running statistics back this up, and he has a languid style of play which can frustrate the fans and make it appear as if he is not even putting a minimal amount of effort. If a player appears to barely be breaking in to a sprint, it follows that people will accuse him of being lazy regardless of his skin colour. People have already mentioned this, but Ozil and Ibrahimovic are two white players with a similar 'casual' style of play, both of which have been accused of laziness throughout their careers. If it was for example Welbeck being accused of laziness, then you would be absolutely justified in calling it out as a lazy racial stereotype, but if someone doesn't bother to run they are going to be branded lazy.
Footballers have been insulted for their intelligence when they play poorly for as long as I can remember. Anybody who has been to a game/seen a match day thread will know that when a striker misses an easy chance, the cries of 'fecking stupid cnut!' are never far behind. Again, just because a stereotype exists surrounding the intelligence of black players, it doesn't immediately follow that anybody questioning a black player for their intelligence is being racist. I never saw Drogba being accused of stupidity, I don't see it aimed at Kante, and one of the players considered the most intelligent in my own clubs recent history (Ledley King) was black. Lukaku is being called stupid because he appears to have forgotten how to make intelligent runs, and seems to have forgotten the basic skill of holding up a football. I think he gets called dumb because he's a large, powerfully built guy who right now looks extremely clumsy with the ball, which makes him look a bit stupid. The big, thick, technically limited target man is a stereotype in football and one which is disconnected from race. I don't see any evidence he's being called stupid because he's black, it seems like lazy assumptions to me. Maybe some of the people you quoted genuinely did call him or lazy or stupid because he's black, but to quote them all and throw about the 'casual racism' tag based on nothing but abuse you see aimed at most footballers is totally out of order.
He gets called fat because he came out and admitted he's a bit fat at the moment, I mean what more evidence do you need? The player himself came out and admitted the fact that putting on weight has impacted his game, and you don't think the fans are going to jump on this when the ball bounces clumsily off him for the umpteenth time in a match? I mean for christ sake, you can see he's overweight, he admits to being overweight, so the fans are going to make comments based on his weight. There's absolutely nothing to support the idea that he's being called fat because he's black. Does anyone remember how much shit Higuain got for arriving at Juventus looking like he had just consumed the North's entire supply of greggs sausage rolls? Athletes are constantly being judged on this shit, because it's their job to be in the right shape, regardless of their ethnicity.
The gorilla comment was totally ignorant, and rightly was called out. That was a genuine example of racism, as is somebody throwing bananas on the pitch or people screaming racist abuse at Sterling during the Chelsea game. Of course not all racism is so obvious, but you can't just throw everybody in the same boat because they happened to call Lukaku lazy, or fat, or stupid .. and then expect them not to be slightly pissed off that you did that without any actual evidence that it was racially motivated. I find casual accusations of racism rife on this board, I find identity politics rife on this board, and I find it utterly ludicrous how you're positioning yourself as a victim after lazily throwing out accusations of racism. You didn't 'stick your head over the parapet', you made a gross generalisation and people questioned it. What else did you expect?