Rules question about shooting through units.

Help please!? I had my first game of 8th ed the other day and my opponent was adamant that you can shoot through enemy units. The rules as written don't seem to support this as it states that "for the purposes of determining visibility, a model can see through other models in it's own unit" (page 179 of the main rulebook) My take on this is that models in any other unit, friendly or otherwise, therefore blocks line of sight. What's the official line on this? Thanks in advance.