why do people find It okay to comment on peoples bodies or the fact they have ed's..

okay so I've been seeing people talk about Arianna grande's Body and how she looks insanely skinny and don't get me wrong I get it, she dose.. but if I was her and people were talking about me like that I don't think it would make me want to recover, id actually be so proud of myself. and I think thats what people without ed's don't get. we don't take it as an insult but more as a praise. I'm not talking about everyone with ed's but more so myself, for instance if my mom or sister or just anyone in general came up to me and said "omg m you look so skinny, you need to gain weight." id actually be so proud of myself for doing so good and being able to get so so skinny that people actually notice and think to tell me to gain weight.. and if I'm going to be frank I don't think anyone with an ed would ever take someone calling them insanely skinny or sickly skinny a bad way they'd most likely take it as praise 9 times out of 10 and even then I don't get why people find it okay to speak on her or anyones body ed or not. also on top of that they're always so rude about it saying things like "I don't know why she would do this to her self she just looks sick instead of beautiful." at the same timeI get they've never had an ed before so they don't get the mentality she may have right now so thats  partly understandable I guess but its also the fact they don't even know 100% if she does have one or not, she could just be on the trend thats going on in Hollywood where everyone is getting super skinny but I'm also not dismissing the fact that there is a higher possibility that she does have one especially with all of the body checking she does..