Try explaining to them that there are PLENTY of used beginner bikes out there in good condition, and that you'll be saving $$ by buying used. Also considering that you're likely to drop it at least once as n00b it's a lot more depressing doing so with a brand new bike. Really, if you're paying for it I don't know why they feel like they have a say.
This !
My first motorcycle I purchased was a 2008 Honda CBR125R. I purchased it "used" with around 17XX km's from the first owner who purchased it from Honda Powersports in Markham. If the word "used" is scaring you from purchasing one, there are many check lists on the internet you can go through when viewing a used motorcycle. For me it had to be low km's, never dropped, overall good condition (cosmetic / mechanical) & proper maintenance done to the motorcycle.
I only rode the CBR about a month and put about 400 KM's on it then sold it after I finished my RTI course, not cause I got bored with it but when my girlfriend got on with me and we tried practising 2up riding in a parking lot the bike wouldn't really go anywhere LOL so I sold it for $200 less than my original purchase price but it was great learning on it.
Now I have a 2008 Yamaha WR250X and it can haul me and my girlfriend around no problem. I plan on keeping this bike forever and purchasing a R6 when insurance goes down a good amount. I'm 21, just got my M2 in May, I have one speeding ticket with a car and getting on the CBR was my first time on a motorcycle... so every time I get on my WR250X puts a smile on my face every time... but different strokes for different folks.
You also have to factor in the costs of owning a motorcycle... gear, insurance, plates, registration, rider training course (if you chose to take it) maintenance, gas, the motorcycle its self etc.
Sorry for the bible passage but I was once in your shoes.