Some people say that it is fine to encourage people to remove their shoes, but one should not insist that they do so.
There is a fine line between insisting on people removing their shoes and encouraging people to take them off. There are a number of things one could say that are subtle encouragements:
We take our shoes off here.
You might like to take your shoes off.
These imply strongly that the host wants the guest to remove her shoes. I do not see that insisting or asking is worse than encouraging. If you encourage people to take their shoes off, then you have started from the assumption that people will be willing to take them off. By encouraging, you apply a degree of moral pressure to comply.
I think a lot of people would not want the uncertainty of just being encouraged. I was dating a girl a few years ago when I was not 100% sold out to the shoes-off rule. She asked me if she should remove her shoes. I told her that we removed our shoes but she did not have to. She was actually uncomfortable at this answer and asked me whether I wanted her to take them off or not.
Sometimes it is simpler just to be straight with people and ask them to remove their shoes. No need to beat around the bush.