If you don't own a home you are not hedged against the housing market.
That's different from being short.
No, the same way that you aren't short on Tesla if you merely don't own any Tesla shares.
> If you own one home you are neutral
Long, actually.
> you can't sell it to make a profit because you always need one roof over your head.
Yes, you can; you may prefer to have a home, but people do in fact live without them, and, further unless you own the most minimal home allowed by habitability laws in the most inexpensive neighborhood, you can always downgrade while still having a roof over your head.
> If you own more than one house, you are a landlord/investor
That's no more true that it is of “if you own more than the least expensive house possible”; it is quite possible to own multiple homes only for personal use value, viewing them neither as investment for resale or things to rent out.
> It would be better for everyone if housing was not an investment
If it wasn't, how would development happen? It only happens because housing is an investment for the first owners, the one building it.
Much like a car - many things are expensive and not expected to go up in value.
Spending money on something in th expectation of being able to resell it later for greater than the cost is, exactly, an investment.
> No, the same way that you aren't short on Tesla if you merely don't own any Tesla shares.
I'm not required to produce Tesla shares every month for the rest of my life. It's not precisely that I need to own "one home" to be "neutral housing", but I need a claim on enough housing for myself (and those I'm responsible for) that I don't have to keep paying market rate for.
Housing as an investment and friction around moving keeps you tied to a particular area, which can be argued is better for a community.
Also, you don't necessarily have to be tied to that area either. You can still treat the house as an investment and rent it out, while you yourself rent a smaller house. In some places in Europe such practices might even be encouraged by the policy (tax incentives etc.)
It would be better for everyone if housing was not an investment.