Here's the quick and dirty run-down of how "Life Insurance as an investment" works.
This is what they do with your example $100 monthly payment:
1. Subtract X% off the top for their fee.
2. Subtract $X for Life Insurance.
3. Invest the rest in bonds.
So sure, whatever you have left over after #1 and #2 will grow in value...sometimes it's even guaranteed, but that might only apply to a tiny percentage of your payment. Here's an real-life illustration:
This was purchased in 1999, with a $523 yearly payment. In 2016, after 17 years of payments ($8891 total invested), the "guaranteed cash value" is... $1400. "But look!" they'll say, "your guaranteed cash value increased 14%! Try getting THAT from a bank!"
If you want bonds, invest in bonds. Skip the middle-man.