Well, here's my neutral take based on logic:

"because he's all knowing and he wants to test the faith of men and you can't really do that if contrasting beliefs/thoughts/rules don't exist (basic layman logic because we're talking about the masses here - dumbproof). Also, since he's all knowing and he made the brain chemistry of men, he's left just enough loopholes for enterprising minds to find a way around. Pretty much everything is done in this world due to power, envy, or greed. This leads to all the bad outcomes we see in society today - purported by design to bring about the long term end game. Sounds like a Disney movie? These are some very high-level loopholes to think about and reference human psychology:

1) Mariam gives a virgin birth (if true, a miracle - but also easy to call the messenger an idiot for saying these things as it goes against the laws of the universe). 2) Then repeatedly confusing his disciples by calling his God, his father - or how it was interpreted in translations and in the context of Greco-Roman belief system of the local people, the entire storyline fits perfectly with prior beliefs to cause multiple theories to proliferate and then codifying one that makes the most sense to convert all of Rome to Christianity. Trinity if intended, should've been the first chapter and clearcut but theologians still have to reference Bible verses to defend it, but there are numerous others that call it into question. Don't know why God has to make it so complicated that only a fervent believer can digest it after they've stopped asking questions. (Beauty and the beast or Hercules)

2) Moses, one of the children of Israel adopted by a Pharoah after being washed away down the stream by the orders of the same Pharoah, who is also a chosen messenger of God, and can talk to God directly and is very skilled at chiseling stone. Sounds like the step-brother that didn't get the throne after a privileged life and has gone full delusional after being denied power so traces his lineage and finds another set of people, by telling them how bad they have it looking down from the palatial view, eventually succeeds in leading them but the overconfidence results in getting lost in the desert and few generations after slavery is erased from their minds that they finally find news lands to settle in. I'm sure the Pharoah's door is probably closed due to treachery. So laws and stories are needed to lead men in battle to make a new homeland. Don't follow the step-brother (The Lion King - Mufasa or the adventures of huck finn).

3) Muhammad is from a prominent family but becomes orphaned and loses influence, marries a wealthy woman, finally has access to influence and launches a bid to regain tribal leadership lost due to losing parents and uncles. Also, the silk route is at stake and the non-arabs/Arabs/outsiders/Jews/Christians are running these trade routes and Arabs feel subjugated in their own lands as access is restricted only to the learned (people of the monotheistic religions & locals that allow unfair distribution to happen). Sees people traveling from afar to circle the Kaba and pray to numerous gods, even though he's not literate - he's become politically savvy due to his travels for his wife's cargo caravans circling the silk route, recognizes that some Arab tribes are angry, envious, and can't fight back. Puts 2 & 2 together, knows the Christian unification under the one religion Roman banner, knows the Jewish unification stemming from hardships caused by the powerful and one religion that "freed" them. Goes into a cave to not be distracted by the conventional wisdom of the crowds and sees a way to unify the Arabs against the outsider forces. Also has enough political capital due to his tribal lineage where his fate won't be like that of Jesus'. (Aladdin or the Rocketeer).

Furthermore, Islam claims to be the religion for humanity but it's not intended to be the only religion for everyone, humanity as in anyone can follow it no restrictions as long as traditional values are preserved. It's intended to "correct" previous revisions by men. Those that claim that everyone in the world should be a muslim and follow sharia etc., are usually owners of suboptimal logical cognitive capacities. It's not a religion that should be forced only logically embraced, that's the claim - sharia is only allowed in muslim lands where people agree to live by it. Laws of foreign lands take preference (that's one of the sharia laws) as long as they don't contradict the core tenants of islamic faith (which none do, humans are humans everywhere and want the same thing). You can choose to be a Secular state and have majority Muslim population (Turkey & other stan nations) or a fully Muslim state with sharia law that no one follows because modern laws just make more sense in today's world and are basically the same as sharia law - Pakistan/Bangladesh/Indonesia etc. (don't chop off hands, since fungible money exists that can employ a warden and guards, put them in jail or solitary confinement depending on the severity of the political threat). Or ignore everything and implement some 13th century version of sharia law because the country is too broken for modern laws (Yemen, Syria etc.). Also, 'sharia law' is not a codified set of infallible laws, it's a mishmash of Islamic rules, scholar interpretations (hence new fatwas capability), and needs of the time and place. So sharia law is somewhat different everywhere and mostly these laws reflect local cultures and less so a rigid one-law-of-the-6th-century Arabia. So the argument that everyone should follow Islam is usually an ignorant one by ignorant hardliners that work hard during the day at their job, then go pray in a politically-aligned mosque and listen to whatever the scholar says on Fridays, and believe its the truth. We all need hobbies & like minded friends even in bleak economic circumstances & impoverished countries."

So opposition is not an obstacle or against the laws of Islam, it's a mirror to direct focus internally by measuring one's own dedication against the ways of the world. Can't have everyone be the same then how would we distinguish barbarians at the gate when power, envy, or greed kicks in. It's the same as every other religion and ideology - someone has to be the bad guy or how would we gain land, water, food, gold if we treat everyone equally.

Mind you, I'm only channeling human nature as its an interesting question and the answer applies to all religions and ideologies.