Most cable internet is a shared service. Meaning, that everyone on your block is sharing bandwidth from a larger pool of bandwidth. When everyone on your block is using the internet, there is less bandwidth to go around. You might not be using all of your "available" bandwidth. But, that doesn't mean that the bandwidth is "available". The other subscribers in your area likely have more to do with your perceived internet speed than the amount of bandwidth you are using.

There is some truth to this one. If I have a high bandwidth connection and my two friends, respectively, have a high and a low bandwidth connection, a file transfer will complete in less time with the high bandwidth friend. That being said, most downloads come from websites and websites have specific bandwidth limitations set to ensure the servers don't suffer service degradation. That's why most web based downloads never go above 2-3 Mbps even when you have 100 Mbps bandwidth subscription.

It stands to reason that adding a second front door means you will get twice as many knocks. It also stands to reason that with more front doors, you'll experience twice as many burglary attempts. What doesn't stand is that having two internet connections makes your network less secure. OPSEC manages both connections with a single device to feed your network. Imagine, OPSEC is watching both doors and an unwanted solicitor knocked on the first door and OPSEC sent them away. The second door would never get open, we know who's knocking.