To what extent is the concept of transgenderism used for bad? I'll mostly be focusing on "trans" women, as they encounter greater barriers than "trans" men (and cis women). We shouldn't call it being "trans" gender, because these people tend to be consistent in forming their gender and do not "transition".
As to fakers, well they don't keep it up for a lifetime - a man can more easily be abusive without pretending to be a woman, and he might be applauded for it... and if they did fake being a trans woman, poorly, they can say "trans" women are bad. It's so typical to say sexual issues are women's fault.
Trans women face greater sexual violence than cis women. I want to note that sexism is any discrimination on the basis of sex, and in the context of not respecting one's gender expression (or traits statistically associated with a certain sex) regardless of sex, it can be used against males by both females and males, perhaps equally sometimes; sexism is not about power itself, as males are not inherently superior (un-inherently I usually find them inferior) to females. Sexism by definition also applies to homophobia.
While ending all sexism is not a perfectly ethical thing, due to certain small biological differences (there are many differences statistically related to sex, and while there's not enough data on this subject, I don't believe most are inherent but rather a result of behaviors learned as a secondary result of socialization), the pros outweigh the cons because we can't let anti-trans beliefs slip in.
Honestly, cis women joke about having penises and testicles, so non-cis women, given what they go through, should be able to joke about having vaginas and ovaries... and uteruses and everything.
We need to change the culture of consent, as well, to always sensitively ask what gender expression one prefers, and to never assume one prefers a particular gender expression, since factors of coercion usually exist for gender expression - though this is more true for males, that they have less say over their gender expression.
I'm not denying the issues that men pose, rather I'm highlighting it as fact. And trans women are not men. Trans women face more dire versions of the issues regular women face, and with added othering from normative women.