这里however作副词,前后都需要逗号,作插入语: Some people, however, maintain that...
这里不能用whereas代替, whereas是连词用来连接2句话,这里只是一句话,需要的是副词。
如果要用whereas, 应当和前一句连在一起, 前后形成对比, 比如:Some believe that watching TV at home is safe and a good way of relaxing, whereas others maintain that...