When did tight hamstrings become a crime? I recently caught myself cueing, "if you need a block then frame your front foot with your block". I've heard this in many, many yoga classes. As it was coming out of my mouth, I felt a "scratch the record" screech inside. I would've rather said "please" use your blocks. Blocks are available to us in class for a great reason. They help us to achieve space in our body so that we can send medicinal breath throughout. What does that mean? It means, if you're limbs are short (or tall), if your muscles aren't ready, if your hips are not open and your struggling in a pose, then you will be holding your breath. If we are holding our breath then we will never create the space in our body to breathe which encourages more flexibility. To teach the body how to become more flexible physically means to have small incremental changes until we reach the point that we can be in a pose and breathe in a pose and release the block. Then as your PRACTICE (that's why we call it that) evolves, we slowly but surely will find more room to move and to fill the spaces of the body with breath.
So, PLEASE, use the block. ENJOY the block. And don't shame your hamstrings.