Borrowing figures from the literature
The issue here is not "laziness"; the real issue with reusing figures from the literature is that, without appropriate permissions, you do not have the right to do so.

If you reuse a figure in the literature without the appropriate permission from the rights-holders, you are effectively stealing their work, which is not allowed. Therefore, you need to make sure that you have gotten the right to use the figures, and have the proof to back it up if challenged. Normally, for scholarly works such as theses, such rights are routinely granted and cost-free. However, you need to check with the publisher (or author of the paper, if she holds publication rights) before using the figure. Then, next to the figure you are reproducing, you'll need to have a statement such as "Figure reprinted by permission of X," where X is the person or institution authorized to grant reproduction rights.