Well first, there are a couple different aspects of this discussion. One for total strangers and another for close friends and family. You can choose your friends but you are stuck with family. On the other hand, strangers are of little consequence anyway.
The vast majority of other runners either don't even notice you and don't care what you look like or how you run or they may even know where you're coming from and empathize completely. How or why they look at you or past you or through you shouldn't matter at all. They are not looking askance. They are simply looking. Their assumptions are based on a mental model of what a "proper" runner should look like and they mean no harm if some comment makes you feel uncomfortable. Those folks just lack a bit of tact is all.
Now, there is a small subset in any sport, let's call them testosterone junkies, who are not merely competitive but openly combative. They look askance at everyone who is not in the top 5% of a race. Older runners, even if they can score well within their age groups are also the subject of scorn. They consider that to be a phoney race category. Only those on top of the game are given any respect. You can safely ignore these people. They will be taken down several notches sooner or later. In fact, I've noticed that they are the most likely to quit competing when their "skills" begin to diminsh.
A much larger subset is welcoming and supportive. They are looking for friends, kindred spirits. Introduce yourself to any and all you meet at a road race. A few kinds words and not a defensive reply will diffuse any misunderstanding. After the race is done, compliment everyone on a good race whether it was or not and the next time you see them you'll have a friend in the crowd. They multiply this way.
The real problem comes from those closest to us, at least in the beginning. If this is a new aspect of your life and not theirs, you're telling them you want to change from the person they are familiar with to someone else. There is some measure of fear that you will look down on them from the superior fitness perch. There is some measure of envy that you can now do what they can't when they know they should. There is the realization that you had the fortitude to do the hard work to acheive what you did and that if they tried to follow, they could fail where you succeeded. So they might want subconsciously to see you fail in order to asuage their feeling of inadequacy or make you feel in some way that what you have accomplished is not that important. To diminsh you is an attempt to retain the status of your past relationship.
In time this will change. You just keep doing what you need to do for you and let them know, first that it doesn't change the relationship and second that their criticism is unfounded. And if their remarks are smarky and snide, let them know in a nice sort of way that it is unwelcome. It will stop. They will accept the new you. They may even follow.