Since I have to get up at 4 AM tomorrow, which is about five hours from now, I will only deal with two of these, maybe three.
First, slavery. As a general rule, the Bible discourages but does not prohibit slavery. In Torah (the Jewish law), a person may sell him/herself into indentured servanthood for a period of time (usually seven years) to pay off debts, and can choose to remain a slave after that if s/he desires, but there are a host of regulations concerning how all of this is done, which are designed to protect the person entering into the indenture or slavery. Since people generally did not work for monetary pay unless they were day laborers, anyone who was an "employee" was essentially working in return for room and board, which is essentially the effect of slavery. In Greco-Roman times, most professionals were "slaves," in that they worked for a member of the nobility and had no say in what they received, how they were treated, or whether they could quit. It was to this situation that the Epistles discuss the idea of how one should, as a master, treat a slave, or how one should work for a master as a slave, and the general rule is, the master treats the slave the way he would treat himself, and the slave works for the master as if working for God—whether or not the master happened to be Christian or non-Christian, nice or mean. Paul also states at one point that if a person is able to purchase his/her way out of slavery, the person should do so. None of which has anything to do with the heinous practices associated with slavery in the antebellum US, or the way slavery is practiced throughout most of the world: the Bible clearly considers such slavery to be unjust, because of the way the slave is both measured (as being less than human) and treated.
Second, having multiple wives. Polygamy is only part of a general issue, which is what God desired marriage to be. The clue to this is found in Matthew 19, where Jesus discusses divorce, that God allowed it in Torah because of sklerokardia. When Nathan berates David for having taken Bathsheba, he attributes God as saying that if, among other things, David thought he didn't have enough wives, all he had to do was ask for them, and he would have obtained more (II Sam. 12:8), but that would also have demonstrated sklerokardia, because David's heart would not have been open to his present wife(s). The Bible clearly has a view as to what marriage is supposed to be, and both polygamy and divorce were concessions to the hard-heartedness of humans before Christ--concessions that are no longer acceptable, because there is no excuse, with the Holy Spirit in our hearts, for hard-heartedness.
OK, bacon. Why God banned bacon in Torah is something we could discuss at another time, though it isn't too much of a stretch to assume that a God who was smart enough to create the universe would be smart enough to know about trichinosis--nevertheless, it is evident that it is one of the many ways that the Hebrews were to differentiate themselves from the Gentiles. However, the ban is lifted by Christ, both in His own teachings and in those of the disciples, and the reason is also clear: the differentiation was no longer necessary, because in Christ there is no distinction between Jew and Gentile, between slave and free, between male and female--each has a position, but ontologically there is no longer any difference, because in Christ they are all part of one body, the church.
The fact that people, who've had centuries to do it, can come up with justifications for their choices doesn't change the fact that this is what they are doing. Constructing justifications for not following clear instructions, in some cases explicit commands, that are no longer acceptable.
This: "The Bible clearly has a view as to what marriage is supposed to be, and both polygamy and divorce were concessions to the hard-heartedness of humans before Christ--concessions that are no longer acceptable, because there is no excuse, with the Holy Spirit in our hearts, for hard-heartedness."; doesn't even sound convincing. It's a superficial justification for no longer engaging in the polygamy that is common and accepted in the Bible.
Same goes for the bacon argument. I missed the part where Jesus said it was OK to eat bacon now. The original reasons for the rule aren't hard to understand, given the times. Things have changed and now we know better, and behave accordingly. Regardless of what the Bible says. Because we pick and choose.
As I said, thank god. Because if we didn't? That bit about killing your child for taking up other gods, and killing witches, and other fun bits? Those are very clear commands and aren't optional.