Keep in mind, he is not telling us to never shoot these five things. He is telling us not to include it in our portfolio when we are presenting it as our best work. Here are the five images:
2. Homeless people
3. Dead trees or tree stumps
4. Anything or anybody on railroad tracks
To find out why, you'll need to watch the video. I agree with his reasoning for not using these images in your portfolio. But, don't get discouraged. He is not saying to never shoot these subjects.
I do firmly believe you should photograph what interests you. There's no reason to take the joy out of your creativity because you've been told not to use something in your portfolio. Your portfolio is a tool for getting jobs. Keep it to your best works and avoid these subjects. For yourself and for your sanity, though, photograph whatever you like and share it as much as you'd like for the enjoyment and for practice with your equipment.
I highly recommend watching this episode, then reviewing your portfolio and pruning it according to their guidelines. See the episode here.