If straight actors shouldn't play gay roles, then gay actors shouldnt play straight roles, right?
That doesn't strictly map because the authenticity gap being noted in this thread doesn't cut both ways equally. Queer folk know a lot more about straight culture and straight-passing than the reverse, because it's in their face all the time and can even be necessary for safety. The reverse isn't really true. So it's a lot more likely that queer actors know how to play straight than the reverse.
This is similar to why people from minority cultures tend to be able to code-switch into the standard dialect of their society on demand, whereas people from outside those minority backgrounds don't tend to be able to convincingly do the reverse. For example in the US, many AAVE speakers are perfectly capable of switching to General American English because being able to talk like the hegemonic culture is useful or even necessary for survival... but there's not many people who can convincingly switch into an AAVE they didn't naturally grow up with.