I agree. In some ways, tools like Macaw do promote laziness. You could compare it to the slicing tool in Photoshop that web designers used to use in the late 90s.

However, both design and frontend development are becoming more specialized roles--especially for large web applications. A designer may be proficient in CSS/HTML but it may not be her forte. She may spend most of her time in design software creating wireframes and mockups and a smaller amount of time actually producing CSS/HTML. Furthermore, some large web applications are so complex (in terms of javascript and ajax) that production HTML/CSS is only written by frontend developers.

Therefore, a tool like Macaw is brilliant for a designer who wants to quickly produce actual working prototypes to show interaction, responsiveness, and animations to developers. Simply delivering static screens to developers is not enough anymore.

And, I'm not sure that designing all in the browser is the best approach, especially if you're working on a complex web application. Designing in some design software allows you to brainstorm and iterate through many different design ideas before settling on something.

Furthermore, Macaw doesn't take away your job of writing CSS code. You still have to organize DOM elements and set class names.

PS Macaw didn't pay me to write this. I just think their product is very compelling for rapid prototyping.