D.B.
This is typical of this transition into 6th grade. Did you child have several teachers in 4th & 5th? If not, he may not be used to having different teachers to "report to" and not just a single teacher looking over him. Sometimes teams of teachers work together to make sure tests and big assignments aren't on the same day, sometimes they don't.
He does need to up his game here. It's not clear from your post whether he's lost and confused, or going through some social adjustments or perhaps some puberty-related distractions which just make him not care as much. So, while it's his responsibility, most kids need some parental help/prompts to get them to ease into it. And, as you have identified, you have a parenting problem here because your husband is not at all on the same page as you. Maybe he hasn't transitioned to middle school either, or maybe he forgets what it was like. "Pressure" is forcing a kid to get all As; it's not telling him he has to fulfill his responsibilities. So if it's okay with your husband and son for your child to have the natural consequences of blowing off the work and getting on a homework contract, or getting low grades, then sometimes that has to be allowed to happen. I know it's not ideal, but no 7th grader ever got kept out out of a good college because he got detention or had to go for extra help either.
My suggestion is that you two set up a conference with the teachers or the guidance counselor so that a) your husband takes it seriously and b) the school can clue you in to supports that are available to help kids get organized. This will also give the school an idea of what they are dealing with in terms of your 2 different parenting styles. Yes, there's a website, but what else is available to give kids the organizational tools they need to move up into middle school? How can they help a mom who wants to oversee it and a dad who doesn't want to do anything but let the kid make the adjustments when he doesn't like the consequences? Maybe there's a happy medium that everyone can buy into.
I do think it's worth your child learning that he's not going to have activities until 8:30 if he doesn't get his homework done earlier. I tend to think you're on the right track - that's how I would do it (teach now, let him take on more responsibility as the year progresses) and your husband's approach would drive me crazy. If he's the type who won't do anything because he thinks you'll jump into the gap with both feet, that's a marriage/parenting issue to be resolved, and it does leave your son being a bit confused, which isn't fair to him. At this age, most tween/teen problems get worse if the parents aren't on the same page. This would be a good time for you two parents to present a much more united front to carry you through this and more serious problems that are going to present themselves pretty shortly.