Imagine you are a teacher. You have two students whom you adore and love as if they’re the children you never have. Now your students can never be romantically involved because it would be labeled as “incest”.
Does that sound stupid and ridiculous? Congrats, you are Raiden and that’s the logic antis use to attack shippers, calling them “weird” and “nefarious” and a variety of names while they are the ones weirdly hung up over a fictional, unproblematic ship.
Liulao as a ship is about as vanilla as a ship can get: no age gap, no power imbalance, no manipulation or other issues, just pure love, trust and a deliciously twisted fate. Star-crossed lovers, they may even be called.
So, if you hate this ship, go ahead and say so, and be done with it. No need to make up excuses just so you can feel morally superior when attacking the ship and its shippers.
And don’t get me started on the whole “cousin” mistranslation. It is tiring!