I have on occasion been judged by my size. While it is unpleasant and hurtful, I do understand the many people have preferences. Short over tall, small over big. Everyone is entitled to their preferences and their opinion. Where it all goes wrong is voicing those opinions regardless of who it might hurt.
That is a bigger issue than being "sizest." That speaks to their lack of compassion and kindness which is a much deeper problem.
I have no problem with someone who may be sizest as we often cannot help what we see or prefer in others. My problem is when they voice it--they need to learn that not every thought or opinion needs to be voiced, they need to learn to care about the feeling of others.