system
Given the following post, respond as if you're commenting on Reddit:
human
CMV: There's nothing wrong with straight actors playing LGBTQ+ members

I've seen a lot of outrage online every time a casting like this happens. Not just over LGBT casts but also over Fraser's role in The Whale. Argument being that a role should only have went to a heavier guy. "“No matter how well a slim actor might portray a fat person in a dramatic role, they can still, at the end of the day, zip out of that fat suit and reap all the benefits of having a societally-accepted body type. They can absorb the praise of being fat when it suits them, but can shed that skin at will,”  wrote one reporter.  What even is point of acting if every role is only reserved for people who are exactly that in the real life. Only people with asthma get to play asthmatics. You have to be part of Church of Jesus Christ of Latter-Day Saints if you want to play a Mormon.

 Now back to the LGBTQ castings. I get the problems with those castings; offensive performances, you can't really get it if you've never been there and long history of Hollywood not getting the presentation right. A trans actor is obviously going to play the part more sensitively and accurately, but...why is just the mere idea of someone who's not trans playing a trans character offensive? They're actors, they're going off a script and if it's done right with possibly trans people on writer's, director's and advisor chair, what's transphobic about it?  Of course, if a trans actor is a better choice , a better actor than whoever else auditioned, give them the role. But a cis person just playing the part on it's own shouldn't be an issue.
gpt
In the abstract, you're right. There's no reason an actor can't *act* to play a role inconsistent with their real-life identity.

But we don't live in the abstract. We live in a world with context. And in many cases, people with certain identities have been excluded from the headlining spots, from major roles, and from the profession entirely. So when a role comes along that's tailor-made for someone with a historically excluded identity, and the person cast in that role is not a member of that group, it looks a whole lot like continued exclusion.

Of course, you can't tie any individual casting decision to that exclusionary motivation. Like with climate change and extreme weather events, we can only talk about patterns and trends. But if we want to reverse those trends in casting decisions, we have to cast actors from those excluded groups. And a simple way to ensure we don't screw that up is to avoid whitewashing any roles written for those groups.

EDIT: Shamelessly stolen from someone else's comment:   
If you're thinking of responding with something to the effect of "they should just hire the best actor," or "That's what acting is," you should know this important task has been fulfilled already many times over, and you can rest easy and spend your energy on something else.