Zombies being able to kill a cow is just plain silly. These zombies don't appear to be super strong or anything of the sort. Without weapons a human can't kill a cow, your teeth and fingernails won't penetrate the hide.
I liked Dale's character but Dale was an idiot, he simply could not understand where he was. His style of argument and chosen path of debate was never going to persuade a group which is fearful for their and their family's lives.
The prisoner had no ties to the group other than having gone to school with the girls...he was a trusted member of a group of predators, he was a threat to the entire group...there was no way they could let him go. In a situation where you had some authority above the two groups, with power over the two groups you would have the luxury of passing on the prisoner's fate to the higher authority. In the situation that currently exists you should look to how humankind and the rest of nature survives....precedent is a very powerful indicator of successful paths when given options.
By precendent I mean; how would a small group of humans or other animals survive, what survival choice would they make in this situation?
Most groups would drive off the dangerous intruder, if the intruder was persistent the two options are destruction or incorporation.
Driving off this intruder is dangerous in the extreme, because he is a member of a more powerful group and has every motivation to lead that group to the farm.
Incorporating the intruder into the group is also dangerous as he has a strong motivation, and possible reward, for abandoning and betraying the farm to his previous group.
Incorporation is a very risky choice, but it looks like this is the one Rick is going to force upon the group.
Shane is dangerous, Rick is dangerous in another manner...in his own way, Dale was dangerous to the group as well in the way Hershel was dangerous...the inability to understand the situation and act on that understanding.