You are always going to end up creating a schema, whether it's explicit in your tables or implicit within your code. Otherwise you end up with completely heterogeneous data which is impossible to query in any useful way.
This is a red herring.
In a sql db, every single thing needs to fit into a flat schema with nesting done by relations. Additionally, it's very rigid. Maybe you just don't want to set up a laces table, and 4000 other tables for every little attribute of every product. Of course this is not how you would do it in real life, there are better ways. Mongo is one of those ways.
Saying that Mongo is good for nothing is just as dumb as saying that Mongo is good for everything. In 2015, the Mongo backlash is just as tired as the Mongo hype.
Nope, see Postgres (hstore and json).
Though i suppose it gets trickier if attributes may have sub attributes etc....
If you say so.