I'll be the first one to say that the execution of a taboo always matters. Rape, mental illness, war crimes, genocide or slavery can be depicted or executed in a manner that can help contribute to the enjoyment and engagement of a roleplay. However, the way you approach it matters. The tone and how you ultimately convey this taboo matters. How do you frame the taboo within your RP? Does it play an important role in your narrative or story? Are you deliberately focusing on the merits of this taboo in any way? If so, why? 

Luckily, we do have a good public case study example of how [i]not[/i] to approach a taboo topic with nuance on RPGO. The GM hasn't been on this site for 3 years so I'm confident I won't be engaging in any harassment or character attacks in any manner whatsoever. 

[url]https://www.roleplayerguild.com/topics/92294-the-rape-of-nanking/ooc[/url]

The link above demonstrates all of the common problems when writers fail to understand taboo topics in a way. 

1) Not treating a sensitive topic with maturity or respect. 
2) Deliberately including game-play mechanics or encouraging players to engage with the taboo topic in a disrespectful manner.
3) Deliberately glorifying the taboo in an almost celebratory manner or conveying it in such a way that is disturbing to say the least. 

All of these factors contribute to making the RP above absolutely ignorant and lacking in nuance of how it chooses to approach the taboo in manner. I think if you want to know how not to tackle taboos on this forum, the baseline has already been set by this roleplay concept. 

It's already been repeated above but I'll say it again. The difference between writing taboos in a novel of your own making and a roleplay is that roleplay first and foremost is collaborative writing and therefore, requires an unspoken consent between involved parties on what taboos they are comfortable with including within the RP. There's also the fact that whilst RPGO is primarily dominated by people living in the US, each and every person will be raised in different backgrounds with different values. What may be considered taboo for others will be considered normal for other people to discuss. Different cultures, societies and religions will have different taboos and different perspectives on how they engage with these taboos.  

That said, the big 'no no' for me is if a roleplayer or writer attempts to gleefully justify or advocate within the text for taboo topics such as racism, rape, genocide or violence, where it imparts upon other roleplayers or readers a positive message about these things in particular. Note that there is a world of difference between in-text justifications or writing characters that justify or advocate these beliefs. 

Anyway, that's all I have to say on this subject matter.