Wrt "externalizing to eveyrone who pays taxes", you'd be absolutely right if I hadn't omitted, for brievity, the reason why you get such large tax breaks and subsidies: you undertake to rent at preferential rates (roughly 20% under market price). In effect, you run a small scale public housing operation.
The subsidies are related to rennovation works you specifically agree to pay for, obviously at the start of the project. The largest tax breaks are in effect at the start of the project as well so the risks, while they do exist, are very limited.
The biggest risk is that you buy a run down property (which rennovation you agree to finance) in a run down part of a town. At the end of the ten years, you might have a reasonable property that's unsellable because the area has tanked even further.
Can't get on the specifics as it varies country to country and even local regulations but as anecdotal evidence, I'm currently looking at a property in my hometown, with a mortgage of 80k€ (cost of mortgage 7k€, 10 years). This property would rent at 4000€/y, resulting in a yearly loss of roughly 4000€ (you read that right).
With local incentives and tax shelters, I would still net 18k€ in gain over 10 years. On a 80k€ property, that's a 21% ROI....