It's true that MTFs face more overt discrimination and hostility than FTMs. Probably because MTFs are more visible. In modern American society, cis women have a wider degree of latitude in dress and presentation than cis men do.
A hundred years ago most people considered it shocking to see a woman wearing anything but skirts and dresses. Famous aviator Amelia Earhart was considered as daring and flamboyant in the 1930s for routinely wearing pants as she was for her very dangerous (ultimately fatal, regrettably!) long distance flying exploits.
Today, there are lots of cis women who never wear skirts or dresses, may not use makeup, have short hair, etc. So in the initial stages of transition, a lot of transmen don't appear that far out of the cis norm.
If you look at the numbers of transpeople who are targets of transphobic violence, I think it's pretty clear that MTFs are more likely to be targeted. But nobody should think that FTMs can't face violent, even homicidal attacks.
One case I remember vividly happened when I was about 11 or 12. I read about it in the newspaper and it really caught my attention, even though I was pretty clueless then and didn't understand what it meant or why it had such an impact on me. A young trans man, Brandon Teena, was beaten, raped, and murdered by his lowlife "friends" when they discovered he was trans. It all happened in a small town in Nebraska, and I couldn't stop thinking about how awful it must have been for him to be isolated in a small town and trying to live the way he wanted in a society that couldn't accept him.
It's worth taking a look at what happened in the case. Here's a link to a short summary:
https://en.wikipedia.org/wiki/Brandon_TeenaThe event was made into well-received movie, "Boys Don't Cry," which I saw when I was about 18 and my feelings about gender identity were really starting to take shape. The movie brought back all the creepy feelings I remembered from when I first read the bare-bones news accounts in the newspaper as a kid.