LOL yes the only possibly reason could be yet another Apple conspiracy to drain your battery intentionally. I mean

some of you REALLY need to be on some meds around here Im convinced.
This has been discussed to death already. It is an intentional "feature" of iOS11. Remember, MR people are the 1% of 1% of Apple educated people. Most people do no physically turn off wifi when leaving the house or office but leave it on and it reconnects when they get to the office or get home. Even I dont as I want to be on wifi at home or work not cellular data as wifi is much faster for me.
The average soccer mom wants to be able to disconnect from wifi and it magically reconnects when they get somewhere else with wifi and a known network to not suck their data plan. That seamlessness is what Apple is. Wifi being on uses a negligible amount of battery life if not connected.
All you have to do is 1 extra click into settings and tick the wifi off button and it wont come back on. Or if you forget the saved network it will not trigger the connection back on. It ONLY connects to previously networks you connected to, and you can easily tick forget that network. There is no security flaw but a user flaw.