I do not believe that giving vulnerable people more rights and better protection in any way erases anyone else.
Erasure is most commonly a consequence of being ignored. People who aren’t represented, and are treated as though they do not exist are erased all the time, and for anyone not affected it can be an entirely invisible process. If certain kinds of people don’t show up in the media we consume, and have put in front of us, we may have no awareness of them.
Our sense of what is normal has everything to do with what we see and hear on a daily basis. If what we encounter is mostly white, straight, cis, able bodied… we may well end up internalising this as normal and being pretty oblivious to the very existence of people who are not those things. At the same time, not having representation, not seeing yourself reflected in your own culture is lonely, alienating and disempowering, amongst other things.
When representation exists but doesn’t come from the people being represented, that can also lead to erasure. Most films are written and directed by men. The women in those films do and say the things men think, or wish women would do. We see women on the screen, and it seems as though women are present, but what we’re really seeing a lot of the time are male fantasies. That’s erasure. Yes, I do think anyone can write about anyone else well and effectively, but if you ‘learn’ from other fantasists, as so many do, then you don’t get realistic representation. I give you female bodies in conventional comics as a case in point.
Similar things happen around stories about disabled people heroically overcoming their struggles, when that’s been created and presented by able bodied people. It’s what happens when cis people write about trans characters all too often as well. Further, when marginalized people do get the chance to speak for themselves, they’re often sorely limited in what they are allowed to do – black authors only being allowed to write about race, queer voices only wanted for stories of coming out and dealing with prejudice and so forth.
Erasure happens when people are not allowed to speak for themselves. It happens when cliches and stereotypes are repeated by people whose only experience is of seeing those things. Erasure happens when people don’t do their research. It happens when areas of experience are ignored and voices aren’t included.
And as an aside, a person worried about female erasure might choose to put a female character centre stage. A person worried about lesbian erasure might undertake to put some visibly lesbian characters into their massivly sucessful book series. Naming no names, because that’s also an opportunity to illustrate how failing to mention someone functions as erasure.