There is too many "ifs" in settling in another planet. What if human biology doesn't endure the life in that planet. What if that worldlike planet had some kind of harmful bacteria that wipe humanity in no time. What if the plants produce toxic fruits. That list goes bigger.
My point is, a fresh start may seems like a wonderful idea. But we don't have enough information about space and the other planets. On the other hand, humankind is a badass intruder whom likes to vitiate. We have to change it first.
There are a lot of ifs in trying to do anything that has never been done. That shouldn't stop us from trying it.
Of course ifs shouldn't stop humankind, it couldn't exactly. What i say is to gather more information and change our vitiation behaviour. It doesn't make any sense to go some place to die from food poisoning or vitiate all the nature because of our actions.