limiting by rep is an arbitrary barrier to entry

Like any treshold is arbitrary, of course. The intention is to help constitute a "proof of human". With no barrier, it is proven that 30 suckpuppet accounts can be created by one entity and take control of STEEM just by means of SP brute-force.

STEEM is a blockchain, but it is also a 4 year old HUMAN community, so there should be ways to incorporate the human factor or the "proof of human" on the witness electoral process.

It could be a "non-issue" to create a witness account with non-rep like 4 years ago. But now in my opinion, it just doesn't make sense to allow such a thing.

If REP can be gamed as factor, at least it demands some effort/time and time is a factor that could be used to protect the chain in case of an attack.