Different game starts -- why do people object?

[zinc]

Some people seem to object to starting the game with 10k money or starting with forces.

Is there a reason that 5k makes for better games?

It may be easier to do an early game "rush" on opponents with the larger amount, but they have the same money to build troops/base defences.

[Ripsn]

starting with higher resources makes it easier to rush and end a game in the first 30 seconds.
10k res + units is recomended for private games and beginner players, but in most dedicated / public lobbies the players like to start with standard rules (5k - mcv)
you will find that this is the same with most online RTS games

[-Jes-]

The random nature of starting units (balance- and composition-wise) is generally frowned upon in a game of skill.

[kr1egor]

10k would be too much spam early, with 5k u have to make good decisions regarding ur economy or firepower

[Hiro]

I think another reason is that starting with no units gives you complete control over your build order, and therefore makes the metagame more interesting because you don't know what your enemy will get first. If both of you start with a few tanks, then you both know you immediately need some anti-tank defence, and so you know that any reasonable player will be getting that and not dogs/riflemen etc.
Standardising can also be good because it gives people a chance to practise their build orders and timings, and therefore tournament matches can be more exciting faster as people know what they're doing with the starting resources. As for why 5k specifically? I dunno. It seems like it's a good amount because it enables you to get your power and refinery and one producing structure of your choice right away, but isn't enough to build an army without gathering some resources of your own first. That and 5000 happens to be a nice round number haha.