How does the only actual instance you mention impact your life?

It makes my work and the work of every other medical professional vastly more difficult. It causes direct physical harm for some. It causes the patient distress when we have to use giant needles to get venous access. As one example.

The frequent flyers in cardiac wards I described earlier fill up the limited time of specialists with bullshit. Those who add on blatant science denialism add hours of fighting and stress to already packed schedules.

Are fat children harming you?

I find child abuse distasteful, sue me. I was a fat kid and I get to watch the same cycle repeat itself. I also get riled up when I see someone kick a dog. Does that make me a snowflake? For not being 'tolerant' of alternative parenting styles?

Is scientific ignorance of these parents directory impacting your life?

There is a non-zero number of cases where obesity related illness has directly led to the death of one or more parents, leaving a child or children orphaned. That's reason enough to oppose science denialism. Stopping kids from growing up fat and sick is reason enough.