You just refered to a living breathing person as a "thing", there is nothing wrong with her appearance.
Not everyone can be a supermodel, just like not everyone can be born a certain gender,"race", or sexual orientation.
Miss Lohan looks just fine imo and I am not even a fan of hers or her movies.
Yeah, it's important to treat people well, however "This is why we can't have nice things" is just an expression, so I wouldn't get too caught up in breaking down its intent.
As to not everyone being a supermodel - of course, however Lohan is an actress, an entertainer, and her looks are her main asset, the quality that allows her to have her wealth has always been her appearance, she is not some greatly skilled actress, but she at one point was cute, then sexy and that got her gigs.
As to lookism, if we were laying into her looks and she was a fry cook at McDonald's I'd say that'd be unfair, but this is her trade. She put herself in the spotlight to be critiqued, so critiqued she shall be. She has the wealth to pursue any career she wants to now, if she doesn't like getting commented in how she looks, she should get out of the modeling/acting industry - or learn how to act.