Personally, different people under each own circumstances will always have different opinion on eating alone. I guess taboo or not, it depends on how the circumstances are. For examples, it may be considered taboo if you are eating alone in Chinese restaurants which usually offer menu for a family. And yeah, obviously a lot of people will look at you strangely because after all, Chinese restaurants are not those places to eat alone. 

But, there is no reason of why you have to be so self-conscious when you really have to eat alone sometimes in front of the public. After all it is not a crime, and hey, haters gonna hate. 

We just have to shake it off.