It occurred to me that since wizards in 5e are allowed, upon encountering another wizard's spellbook, to copy spells of a level that they can cast into their own spellbook (at the cost of only time and gp), a party with multiple wizards could simply collude and spread large quantities of spells amongst themselves. E.g. "Ok, Jones over there will be the one to learn Fireball as his next target of research, and then he'll let us copy it from him. Jones, what spells do you want in exchange from us?"
Is there any reason for discouraging this, especially from a roleplaying perspective? Would most wizards consider this a very un-professional thing to do? Are there strong societal pressures to avoid sharing one's hard-earned spells even with one's closest friends or allies? E.g. "I'm willing to entrust my life to this other wizard in my party, let him carry my gold, trust that he's not going to stab me in my sleep the next time I take a Long Rest, but I'm not willing to let him copy even a single level 1 spell from my spellbook. That's M I N E!".
Best Answer
Out of Character
The balance concerns are relatively small - Wizards are expected to have a great deal of flexibility. In DDAL organized play, it is not unheard of for people to arrange groups just like this - meet up, go on an adventure, then burn a bunch of downtime in scholarly sharing. It doesn't net the wizards any more total prepared spells or any more spell slots, just more flexibility in filling them.
In Character
Without knowing the setting, the second half of your question isn't answerable. Could it be considered unprofessional? Sure, depending on setting. Societal pressures? Sure, depending on setting.
Using Forgotten Realms as an example, the Red Wizards of Thay are very covetous of power. It's unlikely they'd share spells with anything but their most trusted apprentices, and they're very untrusting people.
By contrast, Silverymoon has the Conclave of Silverymoon, a magical university. They offer sponsorships and tuition help for certain types of people - think of it as a modern university with different colleges with in it, aid programs, and fraternities/sororities, and you're pretty much on target.