Assisted Suicide, why are people so against it?

Probably because "life is a blessing from God" or some other bullshite.

because people are selfish and don't want to let loved ones go.

The potential for people to be encouraged to it by family for selfish reasons of the family.

Or people with psychological issues who would take suicide as a solution to their issues.

Neither of those are good for society. Now, a truly terminal patient taking a morphine overdose on the way out isn't a huge moral quandary for me.

because, god

Giving someone enough morphine (or similar) to die comfortably is fairly noncontroversial, and pain management is a major part of hospice care. Giving someone enough to end their life, though, has some valid points from each side. Firstly, the Hippocratic Oath starts with, "First, do no harm..."
Stopping a patient from breathing permanently could definitely be considered harm. On the other hand, allowing someone to suffer through their ultimate end from a tough, chronic illness could also be considered harm, mainly from an emotional/psychological standpoint. In the end, the vast majority of people fall somewhere in between the two, and the majority of hospice care is geared aggressive comfort measures. As to the bitter end of the patient with a particularly painful terminal illness and giving them enough of a medication with that it cuts their "life" short a few minutes/hours, at that point, I believe the majority of people fall on the side of believing that to be ethical. As to allowing terminally ill patients to elect to end their life before the suffering begins/peaks, I think it's just too controversial a subject to have a consensus opinion on, and the ethical debate of whether all life is worth living and has value comes into play. Again, there are rather valid points from both sides. I don't think they'll come together in those opinions, either.

Quite frankly if that's what they want to do then it really shouldn't be my business whether they do it. I don't have any problem with setting parameters for allowing it (i.e. Psych evaluation, multiple doctor's assessments, etc). But as far as morally, that's not my burden to carry.

I know if it was a family member that was suffering I'd want them to have that legal choice.

People who support legislative measures against assisted suicide for the terminally ill, are disgusting human beings. It's hard to imagine someone would be that evil, but there are plenty of people out there that are.

If you don't support assisted suicide, fine, don't participate, but don't take that option away from someone who is suffering with a terminal illness.

We are only allowed to be compassionate for our pets

Because assisted suicide is creepy as frick.