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...
