I don't think anyone has suggested that sequence and ballroom/Latin can be danced at the same time. Or that people do different ballroom or Latin dances at the same time. However, I do think that people of different abilities should be able to share the dancefloor without intimidation from the better dancers. In the past I have frequently seen beginner dancers doing a very basic waltz, for instance, alongside much more experienced dancers doing a much more intricate version. However, my recent experience is that this doesn't happen so much now and that the less experienced dancers are feeling they are not welcome on the dancefloor. As I mentioned, we were certainly not alone in feeling this on the March cruise.
Also, we, as have others, learnt sequence dancing some years after we started to learn ballroom. We learnt it, particularly, as we had watched other sequence dancers having fun in their dedicated sessions on Cunard ships. There is room for both styles at different times. If you look down on sequence dancing then don't go to those sessions. They should still be allowed to take place for those who enjoy them. And, in my experience, they are often better attended than ballroom/Latin sessions. Possibly because people feel more confident doing the sequence dancing precisely because everyone is doing the same steps.